On 21 Mar 2007 18:34:42 -0700, "
wrote:

My boat has an alternator that has a 16-ampere stator (and voltage
regulator). Is there a formula to calculate the number of batteries
that the alternator can charge? Can it charge two or four batteries
all at the same time?

No.

You will have to either up the amperage (which may not be possible) or
charge the trolling batteries onshore with an external charger.

As to the dual boat battery system, it won't charge both of them
simultaneously - you will probably have to install an A/B switch and
use one as a spare using the other as the boat battery.

The start/run battery will probably draw at least 8/10 amps for the
equipment on the boat plus the engine. That's doesn't give you a lot
of amperage to work with for battery charging - one is about the
limit.

Trolling motor batteries are pretty stable over time and unless you
are looking to use the trolling motor on constant duty, they will last
you a good time on the water - 8 hours or so. I have a 24 Vdc system
on the Ranger and the shortest I've ever had on constant duty was
about six hours and that was right before I changed them.