The Sound Link Mini has a user replaceable battery.
You can order it from Bose, or if you read the Model No. on the bottom of the battery and you can internet search it for purchase. Amazon, Ebay, and other places carry them for purchase.
If you have a Sound Link Mini II that requires disassembly of the whole unit as the battery is not user replaceable. They are also unavailable for purchase. you have to send it in to Bose to test and replace the battery. That Battery has a ribbon cable soldered on it with a board.
I posted a comment on the battery removal guide for Sound Link Mini II on how to purchase a replacement, so look for it under the appropriate guide title.
I have heard people say the earlier Sound Link Mini II’s might have the earlier user removable battery, but I have failed to see one yet.
If you have the Soundlink Mini 2, you can send the battery to Bose and they will rebuild it for $75. It is not user replaceable, although if you are electronics savvy you can remove it.
Problem is there are no replacements out there, and these batteries have a control board soldered to the battery with a ribbon cable. This will require soldering and unsoldering if there was a battery replacement for it. This also requires taking the entire Soundlink Mini 2 speaker apart to remove the board and battery.
If you send the battery to Bose expect a 3 to 6 week turn around for a return, which includes about 10 business days of shipping both ways as its a Lithium battery and can only travel ground. Plus the $75 for the repair as mentioned earlier.
They really did a wonderful job in limiting your options on this item.
Bose Hold this L for us as in Losers!