I've had a few gadgets -- for example, an Instax bluetooth instant photo printer -- that ran off of batteries originally introduced by Nokia for phones around 2

I've had a few gadgets -- for example, an Instax bluetooth instant photo printer -- that ran off of batteries originally introduced by Nokia for phones around 2000 (BLC-1/2), including charging them. I doubt many people buy them for their Nokia 3310 these days, but they're readily available from many manufacturers[1]. I think some old Canon DSLR battery form factor is used similarily. [1] Many manufacturers, possibly a single factory somewhere in China.