Is a battery available for Apple remote?

I poked around a bit in my usual parts haunts and I'm not seeing anyone who sells a replacement battery for your remote, either with just the battery or in combination with the charging port as I would expect.

So if you have the ability to cut off the battery cell from whatever BMS and/or flex cable is attached to it, then it still may be possible to find a compatible battery that'll work.

Lithium polymer batteries like those in the remote are characterized mainly by size. You'll see them listed something like 521540; the numbers correspond to the battery’s dimensions:

52 = Thickness in tenths of millimeters (5.2mm).

15 = Width in millimeters (15mm).

40 = Length in millimeters (40mm).

So the next step is to get out your calipers and measure your existing battery. That will be the maximum size battery you can get that will fit in the existing space, but you can always go smaller on any or all of the dimensions; you may lose a small amount of charging capacity but otherwise it'll work fine.

The tricky part will be the connection between the battery cell and the BMS it's attached to. Normally you'll want to cut off the zinc strips, then spot weld the replacement cell on, but that's going to be highly dependent on what kind of replacement you find, whether it has wires or tabs and/or an existing BMS as well.

Anyway, once you have your dimensions, plug those in to a search engine with the words lithium battery and see what comes up. We'll be glad to help in the search if you come on back and tell us what the numbers are; including a photo of the battery and its connections would help immensely.