On some small outboards that run lights and say they can charge 12v batteries, the charging
circuit is dead simple (coil, rectifiers and a fuse), and they don't put out that much current
, especially when the battery's near full up. There's no regulator, they rely on the 'sturdiness' of a flooded-cell battery to withstand a small continuous overcharge. In fact, for our little Suzuki o/b, they mention not to use this type of charger
or gel-type batteries, which can be damaged more easily by overcharge.
To the OP - have you hooked up your outboard's generator
to your battery yet, and made any charging
current measurements, at different motor
speeds? If your motor
can push more than 1 or 2 amp into a fully-charged battery, I'd say a regulator is necessary.
Some of our friends who have charging outputs on small outboards said that they found it mostly useless, unless they were doing extended motoring at flank speed. I haven't yet hooked up the charger
from our o/b, I just top up with a portable solar