Can Sanyo Eneloop AA 1,900 mAh rechargeable battery be used in a small device which has a small solar panel for recharging? The device currently has AA NiCd 800 mAh.

I do that sort of thing with solar garden lights and it works fine, I'm not sure if it is particularly good for the new cells but it works..

I don't think you blow anything up anyhow

NiCd and NiMH chemistry's have very similar behaviour. Both have a negative-delta-V characteristic when just about charged, and both batteries become resistive once charged (they heat up). Both these chargers normally monitor battery temperature as the method to determine full charge. To answer your question, I need more info. How many wires are coming out of the old battery ?...

Although, I suppose, since you are dealing with such old energies (a 1Ah battery), you could just hook it up the best way you think and hope for the best if you don't care about blowing up your applicance :). I doubt it will explode (but without knowing your circuit.. how can I say exactly).

Yes you can but seems a waste of a nice NiMH lsd battery......

Beautiful batteries. Best LSD on the market.