gaffcat wrote:

I am building a boat and recently started my new Yamaha outboard for
the first time. While the engine was running I measured the voltage at
the battery and the reading was 15.5 volts. I have a 100 amp hour AGM
starting battery and the battery manufacturer reccommends a bulk
charge voltage of between 14.1 and 14.5 volts. Is there a way to
reduce the outboards charging voltage? Will this damage the battery?
I think the outboard puts out about 10 amps.


Reduce the rpm of the motor?

How accurate is your test meter?

The voltage is probably high because the battery is charged, and is
resisting the charge current. If the battery was low, and accepting
current more readily, the voltage would be lower with the same motor
and rpm, etc. Your outboard motor probably does not have a very
fancy regulator on it, typical.

What is the "float" voltage for the battery? A bulk charge implies
a discharged or partially discharged battery.

If your situation does not change, as I suspect it will with a
little use, the only damage would be water consumption in the
battery. Keep it topped up with distilled water and keep the
battery tops clean and dry.

Terry K