The best thing about this type of device is that they often contain a fully rechargeable lithium cell. Usually a small cylindrical one, but in this case a decent flat one with very useful capacity. They're ideal for small lighting projects or replacing cells in some items, noting that the cell itself doesn't have a protection circuit.
The cell checks out at above 280mAh after three charge/discharge cycles and is marked 501547P (50mm by 15mm by 4.7mm).
It's a bit disappointing that decent cells like these are used once and then end up in landfill. At least their material composition is relatively eco friendly if they get that far.
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