This Luxos U dynamo powered bike light has a cache battery that provides backup power for the light when the dynamo isn't providing power, and it also provides power to smooth the USB charging that it also supports. The nominal power output of the dynamo hub that feeds it is 6v, 3 watts.
I have not been able to locate a replacement battery given the identification on the existing, 2-cell battery. I'm hoping to figure out how to remedy this since I have some nearing end of life, and I'm considering buying more of them -- but I don't want to do that if I can't refresh them with new batteries when they need them.
The internal battery pack label reads:
802025p LiFePO4 6.4V 150 mAh 0.96Wh 1710
It looks like 2 (3.2 volt) cells wired in serial with another yellow wire coming off -- a thermistor?
The cells measure 8mm thick x 20mm wide x 25mm long, so it's clear that ID number refers to the dimension of an individual cell.
The only cells I can easily dig up with the same dimensions are similar to these (https://www.aliexpress.com/item/33052412361.html) that is, 3.7 volt polymer lithium batteries, which, if I understand correctly, are more energy dense, but at the expense of operating temperature range and service life.
The device itself is very easy to open up, so if a suitable, less long-lived replacement could be created by wiring together a couple of those 3.7 volt, 300 mah cells, that would be a reasonable replacement.
Would I need to worry about the 7.4 volts that would make, versus the original 6.2? I haven't tried to pull apart the original packaging, so I don't know what that yellow wire is attached to. If it's a thermistor, I assume I can just recycle it by attaching to the new penultimate cell and maintain the same performance. If I understand correctly, these little cells often have overcharge protection built into the electronics between the cell and the leads anyway.