(ET) keeping batteries charged

[Ken Olum <kdo cosmos5 phy tufts edu>]

Batteries are happy if kept at a float voltage of about 13.2V for a
12V battery.  They will take as much current as necessary to stay
charged.  You can accomplish this, or something like it, by getting an
automatic "battery tender".  Of course, you need three of them.  A
simpler system, as Chris says, is just to top them off once a month or
so. Don't overcharge them while you're doing us.

What I actually do is to have just one of those battery tenders, and
move it randomly among the batteries that I'm trying to keep topped up,
whenever I think of it.

                                Ken