Inside a tiny CR425 lithium cell and its odd charger - with schematic

It appears that the CR425 lithium cells are available in two versions. The 3V non rechargeable type with a capacity of 45mAh and the rechargeable type with a capacity of 15mAh, and a quoted 100 charge cycles. I cut a cell open, and these tiny cells have a different construction from the larger cylindrical cells. But a similar chemistry is probably used, as the distinctive smell of classic lithium cells was present. The CR425 code seems to indicate 4mm diameter and about 25mm total length.

I think the cell chemistry is probably Lithium Cobalt Oxide and graphite.

I left one of the little lights on test overnight, and over 18 hours later it is dimmer, but still quite bright.

The charger has unusual circuitry that doesn't use the usual 4056 or LTH7 type charge control chips. Instead it's using a microcontroller with an unusual approach to sensing the charge state of the cells.

I tried charging one of the non-rechargeable 3V versions, and it took a slight charge once, but then failed completely.

Here's the AliX link these came from:-
https://vi.aliexpress.com/item/1005007001559671.html


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