The Sound Link Mini II seems to come in two flavors, one with a battery #061384 with accessible/detachable leads, and another version with a battery labeled 088796. The latter one is extremely hard to replace. In that version, the leads at both the battery end and the small PC board are soldered in with a 4-wire flat cable, so even if you could get a suitable replacement, you’d end up disassembling the entire unit.
I noticed that pictures of the right replacement battery (although they are usually sold out) show the black battery assembly together with the small board, so I’m assuming there’s no other way of replacing it.
Since the USB charger delivers just 5V, the board looks like it holds a DC-DC converter to step it up to 9V or so (although I don’t recognize the part). The battery wants at least 7.4V to charge, and I suspect that that converter is the problem. The battery on my unit went from no problem at all to “dead” in a week, so it looks like more of a charging issue than an actual battery issue.
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