"James Hahn" wrote in message
...
Don't pay any attention to replies that talk about converters.

Obviously you don't know what you are talking about.
With such a setup you achieve two things:
1) one battery will always be drainen slightly more than the other.
2) that same battery will alway be charged a little less than the other
because the charger measures the voltage across both batteries in series.

So eventually that battery will be in a continuous state of being empty.
Imagine what happens when you start the enginge or put another heavy load on
a series of batteries where one of them is empty: the empty one will be
charged by the full one, but with reverse polarity.

Have you ever disassembled a broken battery pack of some device? In 99% of
the cases you will find all cells in perfect condition (charged and all)
except one, which was obviously the weakest in the chain, showing a reversed
voltage.

Meindert