I use a 2300mah lipo in my tranny and no problems. a single charge lasts 16hrs. It tends to drop very quickly when you get to 10v though so avoid letting it get close to that as the alarm that previously went off at 9v doesn't anymore.
I'll usually recharge it when it drops into the 10.x volts
£20 delivered on ebay I think (It was sometime ago)
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