[zepp]

I have an aquazepp that uses 8 x12 volt, dry lead acid batteries. they are wired in two lots of four in series, so in effect two large 12 volt batteries. This is so that it can be switched between 12 and 24 volt.
The charger, or should i say chargers are two 6 Ampere, 12 volt chargers (car battery type), wired in series to give a 24 volt charge.

The 'Zepp hasn't been charged for about 6 months with the batteries left in a near fully charged state, so decided to top them up. Usually the charger will start off putting out around 4-5 amps then dropping to about 0.5 when fully charged. This time, however it started off at 3 amp output, telling me they were near fully charged as expected, left them and noticed that 3 days later the charger was still on 3 amp !!.....I felt the batteries and they nearly burnt the skin off my fingers.
I have unplugged it, let them cool and tried the Zepp. It seems fine but could I have damaged them long term and what may have caused this?
Is it more likely the batteries that were done in the first place?...they were fine 6 months ago., OR could it be the chargers have developed a fault?
What would your reccomendation be for an 'intellegent' charger capable of charging at the required output?