I have had the same problem with Numax, also with a leasure battery you only take them down to 50% discharge, any lower than that and you will damage the battery. 2 years ago I bought 4 105 amphr Trogan deep cycle batteries off the internet, these you take down to 20%. We live aboard our boat and during the Sping/Summer we go off for about 5/6 months cruising. I have had no problem at all, in fact in the information book that comes with them it teels you how to look after them and it also states that after several discharge/recharges they will improve their performance, they have. I have two 70 amp alternators with Stirling regulators, when out cruising I will use about 100 amps overnight, telly, fridge etc, when I run the engine next morning it puts about 95 amps in, it takes about two and a half hours to fully charge them again, I am well pleased with them. Just google Trogan, they cost about £130 each and are a similar size to 110 leasure Batteries.