Have a look at the web site below. The circuitsthere  are simple but they
seem to work. There are over 2000 such circuits that I know of that
have been on the road for at least 2 years.

One thing that might kill them however, is a load dump, whereby the
battery becomes disconnected while it is charging/discharging with a
big current.

I think Harris semiconductor has some info about this.

Tony


PicNPoke Multimedia 16F84 Beginners PIC Tools.

**PLUS** - PicNPlay - PicNPlan - PicNPrep - PicNPost
PicNPort - DT Type Saver - *new* PicNQuiz.
Recent addition - Hex To Source converter.

http://www.picnpoke.com
Email picnpoke@cdi.com.au