Battery to Battery chargers (B2B) and Solar Power?

[aandncaravan]

Today we worked on a Motorhome which exhibited strange behaviour with regular discharge of the Starter battery, to the point it would not start the vehicle. It could go from full to zero in a day.

This problem had only become an issue since fitting Solar Power, the prime aim of which was to keep the Starter battery charged as a Tracker was fitted.

 

We traced it to the way the Stirling B2B works and the way the Solar power had been installed.

 

Some B2B's, like the Stirling units, use a voltage sensing circuit to operate, not a signal from the Alternator. The newer B2B's generally monitor the voltage at the Starter battery and if it goes above 13.2v the B2B assumes the Starter battery is now being charged by the Alternator and swings into action.

Only problem is, many Solar power solutions also charge the Starter battery often raising it above 13.2v. This can cause the B2B to start up and start sucking the life out of the Starter battery, yet the Alternator is not spinning to put the power back.

 

We did not fix the problem for the customer, we don't normally work on a Motorhome where a B2B is fitted, as sooner or later there will be tears. In this case the customer did not inform us a B2B was installed when he asked us to diagnose the issue. By the time we found out, I was too intrigued to let the problem go without knowing what was going on.

However, at the point we discovered the B2B we did inform the customer we would not fix any problem we found, but would try and identify a solution to take back to the Installer.

 

 

The issue was a strange one as the Starter battery only ran down when the habitation battery had been used heavily the night before, by the end of the following day the Starter battery would be dead but the habitation batteries fully charged, even if it hadn't been that sunny.

 

If the van was not used, the Starter battery stayed up to full charge.

 

The customer was convinced the habitation battery was some how taking all the power from the Starter battery via the Hymer/Schaudt Power/charger box. The Schaudt display device was also all over the place with false figures, errors and alarms, "so it must be at fault".

But why did the Starter battery only discharge after a 'heavy night' on the habitation battery and not drain the starter battery continually?

 

What we think we showed was happening is that the habitation batteries were taken down low by the end of an evenings heavy use. Then next morning the sun came up and raised the Starter battery voltage above the B2B trigger threshold so it assumed the Alternator has started up. The B2B 'sees' the Habitation batteries are low so sucks the life out of the Starter battery to charge up the Habitation batteries.

 

We could see the B2B 'running' and putting 15.1v into the Habitation batteries, so we disconnected the 'Battery Master' feed from the Solar regulator to the Starter battery, and the B2B went idle.

Reconnected Solar and the B2B started up.

 

It seemed that if the Habitation batteries were low, and the Starter battery got a Solar 'feed' then the B2B would start with a vengeance.

 

We then put on fully charged habitation batteries and the B2B still started up when it got it's trigger, but only until it sensed the Habitation battery was 'full'.

So in the scenario where the habitation batteries where up to full voltage, as when in storage, the drain on the Starter battery was only short duration and not enough to bring it down.

The trickle from the Solar panel through the rest of the day, brought it back to normal anyway.

 

I would expect the Starter battery to have a very short life in this setup?

 

The owner also complained that when the Starter battery did go flat, connecting his Halfords Starter battery charger to the battery terminals, sometimes took much longer to charge the battery than normal, but not always.

Possibly because the chargers 14.4v charge 'triggered' the B2B to operate which then took out more than the power being put in?

In effect the Halfords charger was probably charging the habitation batteries, even though it was directly connected to the Starter battery?

 

 

We suggested the B2B configuration was changed so it was driven by the Alternator D+ signal, so only ever triggered when the Alternator was running. Actually I did offer to put a string of Garlic around my neck and drive a wooden stake through the B2B, but he didn't think that was funny.

 

 

We identified that his other issue with the 'faulty' Schaudt display units erratic behaviour was also down to the B2B, as the EBL 101 is designed to control/distribute all 12v power, both in and out, then calculate how many hours running time are left at that rate of consumption, etc.

It can obviously only do this if it knows about all power to and from the batteries, yet the B2B bypassed the Schaudt Elektroblock EBL, by going battery to battery.

 

The Schaudt DT LCD display device was displaying alarms that the battery needed to be charged, when it was full. It's calculations probably led it to believe that 9,000Ah had been taken out of a 100Ah battery without it ever being recharged!!!

 

This was made slightly worse, because the owner had wired a Universal USB charge socket directly to the battery, rather than via the EBL power ports. This time a 'drain' on the battery the controller was unaware of.

Good job this vehicle wasn't equipped with a Sargent EC325 that can output 18v to the battery to boost charge it for short periods!!

 

Gone are the days when you could connect any device directly to a battery with impunity.

 

 

If a B2B is fitted, check it is compatible with the other electronics and charging systems, in our experience, it usually isn't.

 

 

 

[StuartO]

An interesting case report, thank you.

 

Presumably the advantage of a B2B charger, if you can get it configured to work safely with the other equipment on the MH, is that when you are driving you get a much more rapid recharge of the leisure battery than otherwise because the B2B makes the engine alternator work harder.  So driving a reasonable distance will give you a reliable way to recharge regardless of any other factors.

 

But if you also have enough solar panels (which will work when you are driving as well as when parked up) to boost your recharge as you drive, is there any real point in having a B2B charger as well?  Only on a really dull day or when driving at night would the B2B do anything you might actually need?

 

[sshortcircuit]

Have you contacted the B2B manufacturer to confirm your findings?

 

My B2B cTEk250Dual, is connected directly battery to battery. Once the starter battery is above a certain level the leisure battery is charged. When solar is providing power after the leisure are charged then charge is provided to starter battery, if needed. Obviously when the output from the alternator/starter battery falls, the B2B switches off. On HU I can use the MH to charge the starter battery and when charged this will bring in the B2B to provide multi stage charging to the leisure battery which is a bonus.

 

When a B2B is fitted, the existing charge circuit through the split charge relay has to be isolated, otherwise you will have the alternator and B2B both trying to charge the leisure battery creating confusion with the multi stage charging.

 

My system has been running for a good few years now with absolutely no problems. Even up in the north the solar maintains batteries over the winter months without the need for a boost charge. A good investment in both solar and B2B.

 

Cross posting with Stuart. I fitted the B2B as a backup which would enable me to run engine and give the batteries a quick boost. Running an engine without a B2B to charge leisure batteries is very inefficient.

Agree an interesting topic.

[Tracker]

Yes indeed, a very interesting investigation and much appreciated information.

 

Main point arising - how best, both technically and cost effectively, to provide sufficient 12 volt power on a modern van to provide power when camping off grid for several days - like at a 5 day show for example?

 

Maybe a large solar panel(s) using a high quality mppt regulator set up to split charge between the primary leisure battery(ies) and the secondary starter battery is still the simple way forward to avoid potentially costly problems?

 

 

 

[StuartO]

Tracker - 2016-06-22 9:11 AM.... Maybe a large solar panel(s) using a high quality mppt regulator ......

 

I was chatting to my respected solar technology man recently and he questioned the real need for an MPPT regulator on cost effectiveness grounds arguing, as I remember and understood it, that in terms of optimising solar output it was more important to install diodes in the connections between each panel, to ensure that when some panel or part panel is in shade (eg behind the branch of a tree) the output of the parts of the panels which are generating is not lost through the shady ones.

 

The types and combinations of electrical kit to generate 12 volts which you can buy these days is almost mind boggling (EFOY, B2B, solar, MPPT etc etc) and this case report illustrates the difficulty of choosing the best combination for your pattern of MH use and then also getting the compatibility of the installation right.

 

[aandncaravan]

sshortcircuit - 2016-06-22 9:06 AM

 

Have you contacted the B2B manufacturer to confirm your findings?

 

My B2B cTEk250Dual, is connected directly battery to battery. Once the starter battery is above a certain level the leisure battery is charged. When solar is providing power after the leisure are charged then charge is provided to starter battery, if needed. Obviously when the output from the alternator/starter battery falls, the B2B switches off. On HU I can use the MH to charge the starter battery and when charged this will bring in the B2B to provide multi stage charging to the leisure battery which is a bonus.

 

When a B2B is fitted, the existing charge circuit through the split charge relay has to be isolated, otherwise you will have the alternator and B2B both trying to charge the leisure battery creating confusion with the multi stage charging.

 

My system has been running for a good few years now with absolutely no problems. Even up in the north the solar maintains batteries over the winter months without the need for a boost charge. A good investment in both solar and B2B.

 

Cross posting with Stuart. I fitted the B2B as a backup which would enable me to run engine and give the batteries a quick boost. Running an engine without a B2B to charge leisure batteries is very inefficient.

Agree an interesting topic.

 

 

 

 

It sounds like your CTEK works the same way, by sampling the voltage at the battery?

 

Once the new breed of Sterling B2B's 'sees' the Starter battery voltage rise above 13.2v it starts drawing power. But that doesn't mean the battery voltage is actually above 13.2v, only that the voltage at the battery is above 13.2v. As soon as the sun comes up the Solar system will raise the voltage 'at the battery' above 13.3v, when the actual battery voltage might only be 11v.

 

To demonstrate this, get a discharged battery, measure it's 11.8v, or whatever, then connect a battery charger and watch the voltage rise to 14.4v. Now try and use the voltmeter to 'see' the batteries 'actual' 11.8v.

You can't, all you will be able to see is the voltage at the battery, the chargers 14.4v.

 

So anything which uses this method to determine the battery voltage will malfunction under certain scenarios. That is one of the reasons why the 'Battery Master' style devices are flawed, they work on the voltage at the battery, not the actually battery voltage. They can start stealing power from a 'fully charged' battery, when it might only be 11.5v but the Solar charger has raised the voltage to 14.4v and is putting in 0.25amps.

 

 

You write, "When a B2B is fitted, the existing charge circuit through the split charge relay has to be isolated, otherwise you will have the alternator and B2B both trying to charge the leisure battery creating confusion with the multi stage charging".

That is my whole point, you can't if the system is an integrated one. The Alternator charging is an integral part of the unit, monitoring charge current, voltage, etc and making calculations based on this data.

It might have worked 20 years ago with those systems that had a separate split charge relay, but the modern breed of quality Power Controller units have this functionality built in and use it to drive the Fridge, step retraction, Satelite Dish lowering, etc.

Sometimes the wiring reverse path is used to charge the start battery from the mains box.

 

The modern Power distribution/Charger unit controls EVERYTHING, as highlighted above. That is why a B2B cannot be installed on all modern motorhomes unless you understand, in detail, exactly what the existing box is doing and work with it.

The installer on this one we had in, didn't have a clue, yet are one of the biggest names in the UK.

 

Exactly as you say, the B2B is designed for Craft that tend to have very simple power control circuitry. Literally a Split charge relay, a few switches and a Voltmeter. It has come from the Boating World, they don't have sophisticated systems.

 

The modern Burstner with it's portable LCD screen that can be moved from it's location above the entrance door to a Pod on the Dash to tell you the Roof Skylight has been left open when you start the engine, or that step has not retracted, etc. is a World away from the old 1990's Split relay design.

 

 

Also consider that the sophisticated systems as discussed here ALREADY charge the Habitation batteries from the Alternator at the optimum charge for long battery life.

This one charged at 15.1v and a higher current than the battery manufacturers recommend, how can that be optimum for any battery?

 

A B2B might be the ideal solution for some, and the compromise of short battery life be acceptable, but it is being fitted by people who don't understand the Motorhome environment in the detail required for long term reliability.

 

 

 

 

 

 

 

[Guest pelmetman]

Hmmm interesting.......As I'm contemplating one of these B2B chargers for old Horace, as now we spend months on the same site in winter B-) ......

 

We find that if I've not taken him for a run for a month, he can be a bit sluggish when trying to start, especially when some idiot has turned the headlights on for 10 minutes by mistake :$ .......

 

So would a B2B be any better than a bog standard battery charger I wonder? :-S ........

 

 

[Tracker]

Or just keep it simple and carry a spare battery not connected to anything but ready for use if, as and when needed?

[aandncaravan]

Dave, The average Sterling B2B is designed to trick the Alternator in outputting a bigger charge to the Habitation battery than it would normally give. It effectively force charges a battery at a higher rate than it would normally charge at. That is why most B2B charged batteries lose so much fluid and tend to have a shorter life.

 

I assume you just want a trickle charger to top up the Starter battery, in which case a B2B is not the ideal option? If you are so static, possibly on some sort of charge to the Habitation battery, why not consider a Split charge relay 'in reverse' that detects when the Habitation battery is being charged?.

 

 

 

 

 

 

 

 

 

[Guest pelmetman]

Tracker - 2016-06-22 12:53 PM

 

Or just keep it simple and carry a spare battery not connected to anything but ready for use if, as and when needed?

 

A spare battery is a lot heavier than a charger Rich, plus we'll always have hook up ;-) ........

 

 

[Guest pelmetman]

aandncaravan - 2016-06-22 1:04 PM

 

I assume you just want a trickle charger to top up the Starter battery, in which case a B2B is not the ideal option? If you are so static, possibly on some sort of charge to the Habitation battery, why not consider a Split charge relay 'in reverse' that detects when the Habitation battery is being charged?.

 

 

That sounds more like what I need........are there any makes you recommend?......are they simple to install? ........We have the old fashioned zig unit ;-) .....

 

 

[sshortcircuit]

If a B2B is added to whatever age a vehicle is, then the existing charging system has to be modified, otherwise they two systems will be in conflict.

 

Have you consulted Sargent on your findings?

[747]

pelmetman - 2016-06-22 12:41 PM

 

Hmmm interesting.......As I'm contemplating one of these B2B chargers for old Horace, as now we spend months on the same site in winter B-) ......

 

We find that if I've not taken him for a run for a month, he can be a bit sluggish when trying to start, especially when some idiot has turned the headlights on for 10 minutes by mistake :$ .......

 

So would a B2B be any better than a bog standard battery charger I wonder? :-S ........

 

 

Given the age of your van, is it still Insured against Viking Raids? :D

[aandncaravan]

Most Sargent boxes have an external, totally separate relay(s) so are likely to be impacted less by a B2B. However, the same B2B and Solar installation as documented above would most likely still discharge the Starter battery on a Sargent equipped vehicle.

That doesn't mean all B2B/Solar combinations will, some B2B's are D+ driven not voltage sense. The newer Stirling B2B's seem to be adopting voltage sense operating as the default.

 

 

 

Dave, how about a Durite Voltage sensing Split charge relay available on flea Bay (the smallest amp/capacity will do as it is only for one battery)?

It just connects between the habitation battery and the starter battery and a negative, so three connections.

However, you will be 'reversing the batteries' (NOT reversing the battery connections) to what it says in the instructions in that where the instructions might show a Starter battery, that will be your Habitation battery because that will be the 'trigger' battery in your setup. When the habitation battery goes above 13.3v it will link in the Starter battery.

If you put a 30A fuse holder in the Habitation battery side, you can then populate this fuse only when you want to top up the starter battery, once every couple of weeks?

 

Suggest you only put the fuse in when the charger is lightly loaded, as the old Zig's can struggle with two batteries if they are both discharged.

 

 

[Guest pelmetman]

aandncaravan - 2016-06-22 2:07 PM

 

Suggest you only put the fuse in when the charger is lightly loaded, as the old Zig's can struggle with two batteries if they are both discharged.

 

 

That's my worry with adding something to a system that has worked fine for 2 and a half decades :-S .....

 

Upon reflection I think a stand alone charger will be the best option, plus if my Zig unit does pop its clogs whilst we're away, I can use it to top up the habitation battery too.......

 

Thanks for the input B-)......

 

PS how about one of these?......

 

http://www.maplin.co.uk/p/solar-powered-12v-15w-battery-auto-trickle-charger-l58bf

 

 

 

 

[veletron]

Hi

 

I have a Sterling Power B2B on my van - moved it from my previous van and been in use for 6 years. Brilliant bit of kit for a heavy 12V user. Mine is set to Open-FLA and seems to be pretty intelligent about how it charges the batteries - eg it does not stick 14.8V into batteries that were floating at 13.8V already via solar charge. The max voltage I have ever seen from it is 14.8V, max current into LB's @ 40A.

 

The batteries are properly installed with vent tubes and heavy duty cable/fuses.

 

The existing 12V 'on-the-move' charging regime needs to be disconnected. My 12V panel is a Nordeletronica. I emailed their man Franco Zille (with whom I have had previous comms) to get the info on what to remove. On my old tribby there was a solder blob on the PCBA, on the new van, I had to remove an SMD resistor. I replaced the resistor with an inline resistor+switch so if the B2B ever goes belly-up I can instantly re-instate the built in charger. Deffo agree with A&N here - disable the built in charger before connecting a B2B! Should also point out that I am an electronics engineer by trade.

 

Mine senses the voltage at the cab battery, and engages its-self, but it also disengages its-self when the van battery voltage is low. The cab battery voltage is monitored all the time, it also disengages every so often to see how the cab battery is doing off-load.

 

It does seem a little odd that in A&N's case, his customers B2B did not appear to be disengaging as mine does when it determines that the voltage is too low. The power from the panel via its regulator into the cab battery will be max 5A and likely less, so I would have expected the B2B to have pulled this voltage down very very quickly, and disengaged again pretty soon. I would then expect the cab battery to take some time to recover and for the voltage to rise before the B2B could re-engage and 'try again'.

 

My guess here is that the cab battery is weak, and the voltage thus rises extremely quickly when a modest charge is applied, presenting little load, and giving an entirely false indication of the charge level within. The B2B would then 'cycle' - engage, disengage, engage disengage, rapidly gradually depleting the charge in the van battery with each cycle, the weak van battery not recovering its charge via solar, but giving a false indication of SOC to the B2B thus causing the B2B to prematurely re-engage.

 

Depending on the van, its also worth checking how the fridge has been wired. I have seen absorbtion fridge 12V heaters powered via a voltage sensitive relay (to detect alternator running) rather than via the correct method of energising a relay from the alternators D+ connection. In the above scenario the fridge could switch to 12V when engine not running due to charge controller pulling cab battery voltage up and engaging voltage sensitive relay.

 

Nigel

[hallii]

The foregoing does not, I assume, refer to the simpler "battery to battery" charger that simply takes power from the habitation battery when the solar panel charges above 13.2 v and tops up the engine battery as required with around 2 or 3 amps.

 

I have this system fitted and it has worked without fault for some years.

 

H

[Tracker]

pelmetman - 2016-06-22 2:32 PM

Upon reflection I think a stand alone charger will be the best option, plus if my Zig unit does pop its clogs whilst we're away, I can use it to top up the habitation battery too.......

 

I have this set up and it seems to just about cope with the starter battery over winter OK even in the UK!

 

https://www.amazon.co.uk/gp/product/B0089HEFTS/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

 

https://www.amazon.co.uk/gp/product/B007VLMRP2/ref=oh_aui_detailpage_o03_s01?ie=UTF8&psc=1

 

https://www.amazon.co.uk/gp/product/B00LO3202S/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

 

As you are away on EHU, another option is a Ctek type charger - other brands are available - that you can either leave plugged in on a trickle charge or plug it when when you need it.

 

As a guide I generally found that the 5 amp Ctek charger usually put enough back into a starter battery that was too low to start the van in about 5 to 6 hours or so depending on how flat it was if that helps.

 

A spare battery may be heavy but it does not need to be a heavy duty battery for the purpose - and it will add stability to the trailer en route!

[aandncaravan]

Dave, The low power 'dashboard' Solar panels, like that one at just 1.5 watts, give out very little.

 

A much bigger 100 watt solar panel equates to a peak of about 5 amps in mid Summer in the Sahara and a low of about 0.8amps in Glasgow in Winter.

 

Dividing those figures by a 'rough' 100 and you can see that they put out little more than the equivalent of a flea on an exercise bike equipped with a 1970's Sturmey Archer dynamo?

 

Rather than spend your money on propping up a possibly tired battery, why not put the money into a Varta Silver Dynamic LFD90 battery that will stay charged up for 6 months? They have an exceptionally low self discharge rate.

 

 

 

Veletron, You are talking about the old school B2B. As I say in the text, this was one of the new breed, this can charge at up to 15.1v, see manual extract below.

 

You write, "It does seem a little odd that in A&N's case, his customers B2B did not appear to be disengaging as mine does when it determines that the voltage is too low. The power from the panel via its regulator into the cab battery will be max 5A and likely less, so I would have expected the B2B to have pulled this voltage down very very quickly, and disengaged again pretty soon".

 

 

This one changes it's load on the starter battery. Once triggered it seemed to alter the current draw to almost nothing rather than disengage.

 

The manual states, " This unit will not start until the battery voltage exceeds about 13.3V. After that, it pulls the engine battery down to no less than 13.3V. This enables the engine battery to still receive a small charge and ensures the alternator works at its full potential. The unit takes the 13.3V into the control box and then boosts this up to a maximum of 15.5V"

 

If the Starter battery voltage drops, the draw by the B2B is reduced. The Solar systems 14.4v charge seemed to be enough to keep the voltage high enough to stop the B2B disengaging.

 

We didn't spend ages on it as we had limited time allocated, but the real battery voltage dropped to 12.4v (but still showing 13.6v at the battery from the Solar charger) and the B2B was still active.

 

This is different behaviour to the old Sterling B2B units, hence the warning post.

 

Starter battery was only a few weeks old, appeared good, but has been put through a bashing it was never designed to take.

 

 

[arthur49]

aandncaravan - 2016-06-22 12:24 AM

 

 

............. We could see the B2B 'running' and putting 15.1v into the Habitation batteries, so we disconnected the 'Battery Master' feed from the Solar regulator to the Starter battery, and the B2B went idle..............

 

 

 

But 15.1v would indicate a fault in B2B? Max output voltage of B2B is 14.7v or if set for lead acid its 14.4v?

[arthur49]

arthur49 - 2016-06-22 9:25 PM

 

aandncaravan - 2016-06-22 12:24 AM

 

 

............. We could see the B2B 'running' and putting 15.1v into the Habitation batteries, so we disconnected the 'Battery Master' feed from the Solar regulator to the Starter battery, and the B2B went idle..............

 

 

 

But 15.1v would indicate a fault in B2B? Max output voltage of B2B is 14.7v or if set for lead acid its 14.4v?

 

Sorry aandncaravan. Our posts crossed and I see that my B2B is the 'old' model

[aandncaravan]

Veletron, noted your post on the Fridge issue with Solar but didn't really take it in, it is a good point.

 

That, and your earlier comments on the B2B engaging/disengaging, has made me think about the new breed Sterling and fridge operation?

 

If the new style B2B loads up the Alternator/Starter battery as much as it can by dropping the Starter battery voltage down to 13.3v, how will that impact the Fridge operation on 12v?

The entire vehicle will only get a 13.3v Alternator output, not just the charging system.

 

If the Fridge does only get 13.3v, as opposed to the 14.4v 'ish on a none B2B system do you think it would be an issue?

Probably not enough difference to worry about I guess, except maybe on a big Fridge/Freezer ?

 

.

 

 

 

[Steve928]

aandncaravan - 2016-06-22 9:23 PM

The manual states, " This unit will not start until the battery voltage exceeds about 13.3V. After that, it pulls the engine battery down to no less than 13.3V. This enables the engine battery to still receive a small charge and ensures the alternator works at its full potential. The unit takes the 13.3V into the control box and then boosts this up to a maximum of 15.5V"

 

Have you not cut that quote from the manual a little short? In my manual the sentence continues with "(according to the battery type selected)." and it goes on to state, under 'IMPORTANT', that it is the installer's responsibility to select a battery type/voltage regime to match the battery being charged. The maximum 15.5v that you quote is, from memory, for the battery type CALCIUM.

 

Having selected the correct battery type to match my batteries I get a (measured) bulk voltage of 14.4v and a float voltage of 13.7v from my 'new' Sterling B2B, voltages which will neither cause rapid fluid loss nor shorten the life of my OLA batteries as you have inferred.

 

[aandncaravan]

I was just stating that 15.1v was what we saw as that was questioned.

 

However, don't forget it is also the current that the B2B pumps up, not just the voltage.

It is the higher current that will raise the temperatures at the Plates with a risk of increased corrosion and battery degradation.

The gassing from a higher voltage, where selected, is another factor altogether.

 

 

 

[Guest pelmetman]

aandncaravan - 2016-06-22 9:23 PM

 

Dave, The low power 'dashboard' Solar panels, like that one at just 1.5 watts, give out very little.

 

A much bigger 100 watt solar panel equates to a peak of about 5 amps in mid Summer in the Sahara and a low of about 0.8amps in Glasgow in Winter.

 

Dividing those figures by a 'rough' 100 and you can see that they put out little more than the equivalent of a flea on an exercise bike equipped with a 1970's Sturmey Archer dynamo?

 

Rather than spend your money on propping up a possibly tired battery, why not put the money into a Varta Silver Dynamic LFD90 battery that will stay charged up for 6 months? They have an exceptionally low self discharge rate.

 

 

Good point ;-) ...........Both my habitation and starter batteries are getting on a bit, so before we head off across the ditch I'll treat myself to a new set........will the Varta battery be suitable for habitation use too? :-S .....