Two Batteries Connected - Wiring Question

[Mouette]

Hi,

Just a quick question regarding the way my two batteries are wired together. One is a 50 amp hour AGM and the other is an 80 amp hour AGM. The 80 amp hour is stuffed and doesn't hold a charge any more and I am not too sure about the 50 one either. Goodness knows how old they are! I have had the boat 2 years and they were there when I bought it.

The wiring is pretty standard with both negative posts being connected together and the positive of one going to the Number One terminal on the Battery switch and the positive of the other going to the Number Two terminal on the battery switch.

However, despite the 50 amp battery being the good one, it doesn't seem to be holding it's charge all that well either. I am in the middle of my rebuilt engine being reinstalled, so I have the battery charger going to try and top it up but the voltage keeps dropping quite quickly.

My question is that, with this configuration, will the stuffed battery try and draw the voltage from the good one, or and they both knackered and need replacing?

cheers

[smac999]

unless the switch is in both the batteries will have no effect on each other. charge one at time. the voltage will drop from 14.4v to 13.5v when the battery is full and the charger floats. if your battery is droping under 13v while charging it's probably a bad charger

charge each battery for 24h. make sure it's over 13.5 volt. take charger off and wait 24h and measure the voltage of the battery. it should still be around 12.8v