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Always disconnect the main battery?
userPaul in Brum
Posted: 24 April 2016 4:52 PM
Subject: Always disconnect the main battery?
Just joined

Posts: 14

Location: Rapido 962M '02

Hi folks. Newbie here. Just bought a used Rapido 962M (02 plate). Super chuffed. The couple I bought from explained they always disconnect the main battery (engine, B1) to stop it draining when on site, as it continually tops up the leisure battery (B2). There's a solar panel fitted.

Are they right or just over cautious?

Surely when not hooked up, B2 will be topped up by the panel and when it runs down a drive around will charge it up again (or hooking up)?

I hired a new motorhome last year for the summer and it was fine in this way and didn't have a solar panel to top it up. But the couple were clear - B1 can drain and needs disconnecting at every stop.

I've had a read of the manual and it talks about the two batteries working together but nothing to suggest the scenario from the previous owners.

Any and all advice gratefully received.

(Likely to be first post of many...)
Posted: 24 April 2016 6:38 PM
Subject: RE: Always disconnect the main battery?
Keeps coming back for more

Posts: 166
Location: Liverpool, Cyprus, anywhere. Pilote P696D 2021

Never heard of anyone doing that.
The only things that would drain your engine battery are the alarm and the radio unless your van has a very strange battery setup.
What normally happens is that the solar panels top up the leisure batteries and any spare goes to trickle charge the engine battery.
If you are on ehu on site the same applies.
userPaul in Brum
Posted: 25 April 2016 7:46 PM
Subject: RE: Always disconnect the main battery?
Just joined

Posts: 14

Location: Rapido 962M '02

Thanks v much. Yes it does seem very strange. Having our first trip in a couple of weeks - once valeted... - so will take some jump leads just in case and give it a go. There is an alarm but if not activated (which it won't be as one of the sensors has been mangled by a dog - then should be fine. We will see!
userBrian Kirby
Posted: 25 April 2016 10:34 PM
Subject: RE: Always disconnect the main battery?

Location: East Sussex. Motorhome: Knaus Boxstar 600 Street

Normally, when the engine is running, it will charge both starter and leisure batteries. When the engine is stopped, the feeds to the batteries will be separated by a relay, so that the leisure battery cannot drag down the charge of the starter battery. The two would then only be linked again once the engine is re-started and the relay closes to allow charging to begin once more. However, if that relay has failed closed (which can happen if the contacts have become welded together) and the batteries aren't separated when the engine is stopped, it could be the case that both batteries become discharged together.

If your van is on a 02 plate, it will now be about 14 years old, so it is virtually impossible that either battery is the original, probably by now the third of each. Over that time there is plenty of scope for things like that relay to have failed, or for some unorthodox alterations or additions to have been made, such as that solar panel, which may have provided a bridge between the two batteries that should not exist.

If what the present owner tells you about the starter battery being discharged by the leisure battery is true, I would be inclined to suspect that there is a fault somewhere, possibly in the relay, possibly in the way the solar panel has been connected, or possibly that one of the batteries - or even both - is/are exhausted, and in need of replacement.

My inclination would be to contact the nearest Rapido dealer to where you live and ask if they have an experienced auto electrician on their staff, or if not, can they tell you who they use so that you can contact him. Then get it sorted out as quickly as possible. Electrical faults, especially serious battery faults, if not promptly resolved, can result in further damage to either the mains charger, the alternator, or the batteries themselves.
Posted: 25 April 2016 10:38 PM
Subject: RE: Always disconnect the main battery?
Epic contributor

Posts: 1232
Location: North Yorkshire

Firstly may I advise that you would reach a wider audience, and hence more replies, by posting on the "Motorhome Matters" forum.

I can not give advice specific to your vehicle, but as you suspect the recommendation given by the vendors does seem strange.

Personally I would be looking for a fault, such as a welded or missing split charge relay. Does the solar panel charge both batteries, if yes is it possible that the solar regulator is faulty and allowing the vehicle battery to discharge into the leisure battery? However if there is something wrong with the split charging system, and the vehicle battery is low, there is the possibility of blowing the charging fuse for the leisure battery when starting the engine.

Brave man, keep those jump leads handy, make sure that they are big enough for the job, and that you know how to connect them safely. There may be something in the vehicle handbook regarding jump leads.

Your designation of the batteries as B1 and B2 suggests a "cbe" 12 volt electrical system. In this make the split charge relay is incorporated in the 12V distribution board, and virtually inaccessible. Hmmm?
Posted: 26 April 2016 9:51 PM
Subject: RE: Always disconnect the main battery?
Epic contributor

Posts: 1079
Location: Glynneath South Wales


If you are going to disconnect the battery, disconnect the EARTH lead.

Better still, search Ebay for a battery isolator switch, preferably one that clamps onto the battery post. Only takes seconds to connect/disconnect, and your fingers don't get dirty. Initial fitting uses the same spanner as the battery clamp, takes no time at all.

Er ... don't modern cars lose some sort of memory if you disconnect the battery? I don't "do" new-fangled.

userTerry Sankey
Posted: 25 August 2019 9:29 PM
Subject: RE: Always disconnect the main battery?
Just joined

Posts: 18

When locked in a secure barn we have put a suitable heavy duty in line switch in earth cable to the main starter battery under the bonnet of our Autotrail Mercedes Sprinteer motorhome. This stops the alarm clock etc draining the battery which used to happen over about four weeks. The only negative is I have to retune the cab radio each time, but a small price to pay to maintain my main battery. The relay on every motorhome as far as Im aware will disconnect the main starter battery from the habitation electrics once the ignition key is removed.
userDerek Uzzell
Posted: 26 August 2019 7:28 AM
Subject: RE: Always disconnect the main battery?

It may be the case that, as standard, a motorhome’s starter and leisure batteries are not linked together when the vehicle’s ignition key has been removed, but there are devices that deliberately link those batteries to help maintain the starter battery’s charge-state when a motorhome is not being used regularly. The Battery Master device shown on this link is an example

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