JimH wrote:
I am planning to purchase a portable 12v charger/power supply for the boat
rather than installing a second battery. My 12v power draw is negligible
(engine starter, cd player, depth sounder) when not running.

This is one unit I am looking at:
http://www.break.com/movies/houselights3.html

Any recommendations or am I being foolish by not installing a second battery
with A/B switch for my modest 20 foot runabout?


The downside of the jumpbox approach isn't a lack of CCA, but a
shortage of available amp hours. If you wind up having to use that
thing to restart your engine, you will be somewhat Ok if it restarts
right away. If you crank a bit and then discover you need to do a some
troubleshooting to get the engine to fire, try a few things without
success and crank a little bit each time- you may discover that those
"1200 peak amps" are reduced
to the point where you can no longer crank the engine.

This thing is $80. You should be able to buy a suitable battery switch
for probably $25-40.
If you then spend another $89-100 on a medium grade battery (and
another $20 on some cable and connectors) you will still be spending
very little and you will have a standard electrical system rather than
an emergency start device.

If it were my call, I'd go for the second battery *and* the jump start.
:-)