On Fri, 15 May 2009 17:47:00 -0700 (PDT), ransley
wrote:

On May 15, 4:01Â*pm, "BetaB4" wrote:
I posted a question in the newsgroup "rec.boats" about recharging a
lead-acid battery for an electric boat motor after returning from a
boating/fishing trip. Â*The original question was about whether it's okay to
leave the battery charger on for a few days to a week. Â*I found out that,
unless I have the more modern automatic type of battery charger, that is a
bad idea -- due to overcharging the battery.

Then someone suggested just plugging the battery charger into a timer and
setting the timer to turn the power off to the battery charger after say 12
hours.

My question now is,

"If I do the timer idea, could the fact that the battery charger will still
be set to "ON", and will still be connected to the battery after the timer
cuts power to the battery charger, cause the battery to discharge and drain
back through the battery charger?"

I tried a Google search but didn't find too much info that I could use.

Batteries need to be monitored by voltage, not guessing. Your battery
charger may or may not work or even charge properly to 100%.
www.batteryuniversity.com has all the info you will ever need to
maintain them properly, but basicly keep the voltage to low and its
ruined by sulfation, keep it to high and the plates deteriorate.
Battery maintainers take care of these issues and they are cheap.
Knowing proper voltage is something you will always need to know and
check to be sure your chargers actualy are working as intended.

A good 3 stage marine charger (particularly the "mountable" type)
should be safe to leave connected, either plugged in or not.
Some (mainly older units) have "relay" isolation - physically
disconnected when not charging. (or not powered on)