The problem with a switch is that it is up to you to use the switch so that
both batteries get enough charge. Or you need to charge the batteries when
you get home. There are devices that you can put in line with your charging
system so that both batteries always get charged. The most common is simply
a pair of large diodes but unfortunately for them to work really well you
need an adjustable voltage regulator so that you can compensate for the
voltage loss.

When confronted with the same issue I decided that all that complication was
not really worth it. I have a 19 ft boat and we run a lot of electrical
stuff when sitting sometimes. I use one dual purpose group 29 battery and I
replace it every three years. I keep a trickle charger on it in the winter.
It cost a few dollars more than a group 25 or 27. I've never not been able
to start the boat.

If you really want two batteries I would recomend they be the same. That
way they will come close to charging equally when the battery switch is in
the both position.

"Bryan" wrote in message
. net...

"Ed" wrote in message
...
Unless you maintain them, they will both be dead when you want to use
them. Use a battery switch... start and run on one battery (to charge
it) Then when you stop to play with your toys, switch to the other
battery. When you are ready to go home, try and start on the battery you
used.... if it works.. great... it will charge on the way home... if not,
switch to the other and start the engine to get home and then don't
forget to charge both when you get home.

another option... I have 2 batts on my 17' tender and I use a perm
mounted 2 battery charger so they are both always fresh. They will
last longer and within 2 years, they will have pd for the charger due to
fewer battery replacements.

I plan on a dual switch so I can run 1 for the engine/starting and 2 for
house.