Originally Posted by ssullivan
Question: I'm not sure what I'm missing regarding the Trojan T-105's. I did a lot of research
. I read that the 6V T105's are each rated at 225ah. I assumed that they retained that rated when I hooked them up in series to produe 12V. This isn't true?
It is true that each battery has the same capacity, but...
In a typical boat, everything is a 12 volt system, so you can get away with talking about amp-hours. The thing that is getting you is this: amp-hours is only meaningful when everything has the same voltage. You cannot compare the 6 volt amp-hours with the 12 volt amp-hours.
The real physical entity is watt-hours. watts = volts times amps. watt hours = volts times amps times time.
Your T-105 contains 225 AH at 6 volts, for a total of 6 * 225 = 1350 watt-hours. Use two batteries and you have 1350 * 2 = 2700 watt-hours.
But how do you draw the power out? In series, you draw 12 volt power. 2700 watt-hours / 12 volts = 225 AH at 12 volts.
( In parallel, you draw 6 volt power, and 2700 watt-hours / 6 volts = 450 amp-hours at 6 volts. )
If you have four of them, you probably have two banks of two batteries in series, for a total of 5400 watt-hours, which comes to 450 AH at 12 volts. If you sized your charger
for 900 AH (and it sounds like you did), you can put another two or another four batteries, for 675 or 900 AH respectively.