swifty Posted January 27, 2022 Share Posted January 27, 2022 The 110v leisure battery that was supplied on my three and a half year old van let us down last weekend after we had the heating on Friday afternoon and early evening and again on Saturday afternoon. The battery hit 12.2v on Saturday evening and everything went off. It rallied after a while so we were able to put the lights on. When we arrived home the control panel showed the battery to be fully charged and I plugged it in to the mains and today it reads 13.9v so I thought maybe a cell had failed. I put the battery in my car and went to a local battery specialist thinking to buy a new one with maybe a part exchange. However after a chat with the specialist he said the readings were quite normal and I did not need a new battery. The battery is still removed and the reading is13.15v with nothing drawing on it. Is this normal plus also thought the reading on an AGM should have been 14.5v or thereabouts. The specialist seemed to suggest I should not keep it permanently plugged in but rather let it it discharge and recharge a few times. Any advice would be very acceptable. Link to comment Share on other sites More sharing options...
colin Posted January 27, 2022 Share Posted January 27, 2022 The voltages sound about right. IMO the battery should be occasionally put on charge, not permanently, so I agree with the 'specialist'. Without knowing how much you took out of battery (like gas or deisel heater?) it's hard to say why it cut out. Link to comment Share on other sites More sharing options...
swifty Posted January 27, 2022 Author Share Posted January 27, 2022 The shop I went to sells nothing but batteries so I think that would make him a specialist and he didn't try to sell me a battery. The heating is the standard truma blown air heating. I didn't use much gas because the battery didn't last long enough. I was trying to heat the van to number 3 on the dial. Link to comment Share on other sites More sharing options...
Keithl Posted January 27, 2022 Share Posted January 27, 2022 David, I would suggest fully charging the battery then doing a simple capacity test. Charge for at least 24 or more preferably 48 hours then allow to rest for 12 hours. Measure the voltage at the terminals. Now apply a known load, something like a 55 Watt headlight bulb and monitor the voltage every hour until it falls to below say 12 Volts. Multiplying the load (55 / 12 = 4.6 Amps) by the time taken for the voltage to fall will give you an approximation of the capacity of the battery. There will be an exact procedure for this test but the above should give you a good idea of its capacity. Keith. Link to comment Share on other sites More sharing options...
mikefitz Posted January 27, 2022 Share Posted January 27, 2022 Slightly over 13 volts is normal for a fully charged AGM battery with no load after a full charge. The voltage of 14,7 is a typical charging target voltage, the absorption voltage. With suitable chargers you should see this as the battery nears full charge. Is your comment about 'things shutting down' at 12.2 volts correct. A battery at 12.2 volts under load is around 50% state of charge. It may be there is a wiring fault that is causing a voltage reduction in your system causing shut down. One issue that can occur with AGM batteries at a few years old, is loss of capacity. This is due to most charging systems not fully charging the battery, either not a high enough voltage and/or not enough charging time at this voltage. The result is that although the battery seems to have the correct voltages the actual capacity is a fraction of the 'name plate' capacity. Thus a 110 Ah battery may only have 30 or 40 Ah of capacity. The suggestion made by Keith to measure capacity is a good idea. However may I suggest a slight variation of the method. Charge the battery up fully and then leave of float charge, 13.8 volts, for at least 12 hours. This will put the last few % of charge into the battery. The 110 Ah battery at the 20 hour rate should deliver just over 5 amps for 20 hours until completely flat. We will be less stressful and only discharge to 50% in our test Load the battery with a car headlight filament bulb, 55 watts. For every hour the battery is loaded 55 watts will be consumed. Keep a watch on the time and stop the test when the battery voltage reaches 12 volts. At 12.0 volts at a 20 hour rate discharge the battery is 50% discharged. The test does not have to be continuous, just note the time and disconnect the load until you are ready for the test to continue. For example if the test showed that there was 5 hours of run time before the battery reached 11.5 volts we have consumed 55 x 5 =330 watts of energy, or approximately 330 / 12 = 27.5 Ah. Since the test was stopped at 50% capacity we can assume the battery capacity is 27.5 x 2 = 55 Ah. Do not be surprised if the measured capacity is very much less than expected. Mike Link to comment Share on other sites More sharing options...
Derek Uzzell Posted January 28, 2022 Share Posted January 28, 2022 Presumably swifty's vehicle is still the (2018?) SunLiving S70SC motorhome mentioned in this 2019 forum thread... https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/power-from-vehicle-battery/52958/ Link to comment Share on other sites More sharing options...
swifty Posted January 29, 2022 Author Share Posted January 29, 2022 Yes it is. The battery is still disconnected and the voltage has dropped to13.1 Link to comment Share on other sites More sharing options...
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