A500 RTC Battery replacements

[Dingo_aus]

I presume that most (all) memory boards that can with a RTC battery backup actually charge up the battery?

I need to replace my RTC battery and was wondering if I can just replace the original NiCad with 3 AAA NiMH? via wires to  a battery holder.

Are there any problems doing this?  I presume the charging circuit is a trickle charge? and that this method of charging wouldn't be to harmful to the NiMH, and they might actually charge up?

Or is it better to replace them with 3 AAA NiCad batteries?

[Dingo_aus]

That is cool.

So the 3v is enough? and the Lion doesn't need charging I take it.

So you don't connect the "charging" terminal, you just wire the coin battery into the + and - and it works happily?

[Dingo_aus]

Thanks for your help everyone.

I finally got to the shop today and got a coin battery holder.

Whacked it on with a diode and finally my Miggy can remember 2005 and not keep having flash backs to 1978, before it was even born!

[Dingo_aus]

Oops, spoke too soon.

IT seems to hold the time for up to an hour with the power off, after that it loses it.

Any ideas?

With a fresh cr2032 and a diode I am getting 3.00V flat on no load.

This is my board (before I got rid of the NiMH.
http://www.users.on.net/~symes/other/a500/Mem%20Expansion%20and%20RTC%20backup.JPG

Maybe this particular board needs more voltage or something. I have a few other mem expansion boards, I'll whack the setup on one of them and see if it can hold the time.