Replacement Battery for Apple TV Remote A2540

@danj, are you talking about the button cell batteries that older model remotes took? Because this one is completely different; it's a rechargeable Li-Ion square battery with the flex cable and Lightning port attached. I looked around but couldn't find any being sold.

At this point the only thing I can suggest is removing the battery and disassembling it to the point where the basic cell can be identified, then replace that alone, which would involve spot welding and/or soldering. The cells generally go by size and number of wires, so we'd have to know that before trying to locate one.

@charliedavies First thing to do is to pull the battery and get us some good pictures of the front and back sides. The main things we want to know are the dimensions (LxWxH) in mm and the number of wires connecting the battery to the flex cable. That will tell us whether there's a temperature sensor built into the cell itself or if it's just the battery's positive and negative terminals we have to worry about.

Once we know that, it's fairly straight forward to search for the particular cell needed; for example I have some cells I replaced in a concrete float whose dimensions were 3.5 mm thick by 70 mm wide by 95 mm long. So those numbers get combined into a single "model number" to search for; in this particular example the mode comes out as 357095. Searching for that number with the words Lithium Ion gives us sources for that specific cell. Here's an example.

Amazon.com: FCQLR Compatible for 3.7V Polymer Lithium ion Battery 357095 Rechargeable lipo li-ion Cell 3500mAh for E-Book DVD 7 inch Tablet PC Q8 357096 : Electronics

Of course, your battery won't be anywhere close to this one, but that's how you go about finding it; two digits for the thickness, two for the width and two for the length and that'll get you cells that'll fit the physical space. Since Li Ion batteries are pretty uniform in power density, whatever you find should be very close to the original specs for mAh rating as well.

You may not even need to measure the battery yourself; the cells in the battery pack I was replacing actually had those numbers printed right on them, so that's all I had to look for. Note that the battery you find may or may not come with a BMS (Battery Management System) already built into it; if it does have one you'd probably need to remove it in order to use the cell with your existing flex cable and BMS.