Alan: After two big recent outback trips (25,000KMS) I thought I'd throw in my experience with batteries. Like you I went with sealed AGM batteries on separate bank to the starter batteries. Anyway on both trips, the AGMs failed (open circuit). On each occasion I replaced them with straight HD lead-acid truck batteries and those have never failed. Lesson learnt - I'm not sold on AGM for very rough stuff. I's also inclined to think your capacity is an overkill - 300AH should be heaps - particularly with modern energy efficient LED lightning. We run a fridge and a freezer in very hot areas with only 150AH with 300W solar panels. Regards Steve
Hi Steve, firstly welcome to ExPo.
I certainly don't want to make light of your experience but I do want to share this build with Alan.....it is a brave thing to run one battery bank even if it is an overkill capacity......the vehicle below also has done some really heavy tr avel too, Connie Sue, Anne Beadell, Gunbarrel, Canning, Cape, etc, etc but we set it up with only one bank of 2 x180ah AGM (180ah @ 24v) ....either Full River or Ritar....can't remember exactly......4x 68watt Unisolar laminates and a diesel Watts2c Powermaker (2.5kva@24vdc) shown in the rear left locker, to limit depth of discharge and cut in whenever load exceeded 40 amps. There were some big loads too. Large AirCon , bread maker, coffee machine run by 3000w inverter, v2x fridges, sat TV, etc. The first time I checked the hour meter , a bit over a year in service, the Powermaker had only clocked about 120 hours .....these guys free camped in this truck for almost 3 years too albeit in very open country so the solar would have been very effective and also they moved around a bit so alternator charging would also have played a big part.
BTW They changed out the batteries after 4 years purely as a precaution even though they were still showing no sign of deterioration. Remember the pair of AGMs were the only bank of batteries on the truck. I should also mention that battery temperatures were monitored by the Powermaker too so they should never have got hot under load or overcharging .... And my thought is that heat can be a contributing factor in 'open circuit' battery failures.
I think in theory, an AGM by its construction format should be more robust than a typical lead/acid but maybe there was a quality issue there with those that failed on you.
Note that this was the only truck I have ever had anything to do with that runs a combined start/house and while it may sound scary it has worked extremely well in this case with effective monitoring.
Regards John