Over the years I have found lead acid batteries to be rather odd. In one case, a 12V 33AH battery was used to power an equipment that only consumed an amp at the most and the battery was never discharged to less than 60% capacity. Also it was only left in this discharged state for a maximum of four hours.
In spite of this benign regime the batteries never lasted more than 6 months (low capacity, high internal resistance). Yet the same type of battery fitted to a car had no problems. So it does seem that some batteries like to be 'excercised'.
We were going to get some deep discharge batteries which I understood would survive OK, but in the end we changed to NiCad or NiMH, cant remember which.
My advice, for what it is worth, is to look into the lead acid battery options, and if you are not already doing so, evaluate the deep discharge type. Of course, the real answer would probably be to go for LIIon.
