> Does anyone have a design for a charger that can
> maintain several 12volt battries? I would like one
> that could put out several amps, but that will not
> overcharge the batts. I would really like to build
> this myself, both because I am cheap, and because I
> like to build things.
Not built this myself but here's a link to get you started. It's a solar charger but it should give you an idea on how to do it.http://www.redrok.com/electron.htm#charger
> How do I prevent the charger from trying to provide
> too much current when the radios are transmitting.
Commercial chargers have a limit to the amount of current they will provide. Mine has a trickle, 5amp and 15amp setting.
> How do I figure out how long the batteries will
> last? I know that the only way to be sure is to
> disconnect the charger and try it, but I would like
> a rough estimate.
First you have to figure out your average drain. Check the Emergency Communication section for various estimates based on receive vs transmit ratio, or Im sure someone will post the math.
I have a link in my bookmarks at home (currently at work) to a website where you can type in your usage and battery backup size and it will tell you expected run time. I'll post it when I get home.