A4000 battery replacement

[orange]

I'd say you can safely use rechargable AAA NiCd or NiMh. But DO NOT try alkalines, they are NOT designed for charging and might overheat, damage something.. etc
It would be wise to fully charge/discharge those NiMh batts 3 times, just to be safe. BTW, their capacity is probably huge so it doesn't matter if they lose some.
and don't forget to be carefull in orientation.

[orange]

don't forget the great option - using super capacitor, it seems like best solution. the only problem might be high inrush current maybe?  :roll:  and they might be hard to find + expensive.