I think I had a similar problem. I have 2 deep cycle batteries in parallel to make a services battery. I found that my charger was constantly charging at 4 to 7 amps and one battery was getting warm. I disconnected that battery and the charge current went right down. The failed battery seems to have one cell failed – about 10 volts coming out of the battery – and so the charger was constantly trying to charge it.
FYI if your using more than one battery in parallel it is important that both the load and the charge is across both batteries. Otherwise the internal resistance of the batteries and the cables will cause one to be subject to bigger loads and one lower charge rates. This will dramatically shorten the life. When two or more batteries are used in parallel you should for example connect the first battery + to battery number one and the – to battery number two. Where 3, 4 or more batteries are connected you should spread the load and charge as evenly as possible. For example battery 2 has the + and battery 3 the – This will help. Although, technically with 4 batteries you need to have a common ral for + & – which is connected to the input output cables supplying all with the same charge or load.
Sail Save Ant & Cid SV Impavidus.