For the trucks we've had to deal with, the battery is actually part of a chip on the board. It's a Dallas DS12887. Sometimes, it's under an aluminum enclosure (have to carefully cut off) It's usually the biggest thing on the board. You have to be good with a Dremel and a soldering iron if you wanna tackle this job.

Here's a video explaining how to repair the chip. Note that you will have to remotely mount the battery holder somewhere other than suggested because there's not room above the chip with the housing assembled.

https://youtu.be/NdlSfqto_0o?si=WV6f_aKNlFUqNVDJ

One more note, you can buy new chips on their own, but they've not been manufactured in years, so you are counting on a battery that is several years old.