my half-pennies worth, bit late in the day because came on to this site to ask my own question about batteries. I feel there are multiple problems.
Recovering flattened batteries: Try recharging them, nothing to lose. 40 mins driving won't do it. Put on a charger and leave to charge for a few days. (N.B. charger must be compatible with the
battery type - Wet/Flooded, AGM, GEL etc. so best use a decent smart charger). As somebody has already commented, the capacity will probably be reduced by this mishap and therefore their life will have been shortened but hopefully they will get you by for the time-being.
Why were LBs flattened: A few things to check here because there should be safeguards to prevent them dropping so low: [
EDIT: Apologies, I had forgotten Centreman's post describing that the fridge is only designed to use 12v off a running engine since it is an absorption (gas) fridge, so I've deleted the content under this heading! ]
Why was the starter battery flattened: I have read the other comments including about fancy auto switching fridges - it is all beyond my experience. So if it were my MH I would be drawing out how the electrics are wired and configured, and aim to isolate the starter
battery (SB) from the LB circuit. I'd definitely disable any config that switches an appliance over to the vehicle when it is not running. It is so undesirable to allow the habitation electrics to flatten the SB unexpectedly. Not as easy as it sounds though. Not only do you need to check for other appliances and devices draining the
battery, all the possible cross feeds need to be explored. An example that, though not specifically relevant here, demonstrates peculiar interactions:
Solar Technology UK
solar panel controllers have twin
battery capability but if the two batteries that are connected into B1 and B2 on the controller share a neutral/ground (quite common in a MH I would have thought) the manufacturer reports that the controller can get confused and flatten a
battery. Oops, awkward.
Check for stuck vehicle alternator charging relay - possibly embedded in a controller. You may need to remove fuses to isolate the LB side from the LB itself. You'd be looking for an "open circuit" voltage (low and fluctuating) with the engine off and a 13v+ with the engine on.
Battery charging: AGM batteries need a higher bulk charge voltage so will never reach full charge and their life shortened if the charger is using a profile suited to the trad wet/flooded
battery. Could it be that you were never charging your
battery up to max charge? Given the earlier problems with batteries I would want to understand and check the
battery charging systems down to the Nth degree - but that's me!
- EHU Charging: I don't have personal experience of the Sargent PSU2007 but quickly checked its manual and could not find instructions for setting up the battery type. Happy to be corrected, however I have read elsewhere a rant about how caravan and MH manufacturers are fitting AGM batteries with chargers that lack an AGM config.
- Solar charging: The solar charge controller also needs options to select battery type if using AGM batteries in order to maximise the charge and lifespan.
- Vehicle alternator charging: I have not a clue how this is controlled with the latest technologies and this was the question I logged on to ask! Old school, a split charge relay would sort out the connecting in of the LB when the engine is running and isolate the LB when not running.
Something that I am not sure how much to worry about is if the SB and LB are different
battery types. If the vehicle has stop-start the SB is likely AGM, otherwise probably trad technology. MH and caravans have been installing AGM for a while but there will be a mix of technologies in use out there. I am skeptical that all the 3 charging routes accommodate the different
battery technologies across the SB and LB and think we need to be aware of the limitations of the charge set up, almost on a case-by-case basis. Scary!