Funnily enough, the same thing goes for battery “packs” in UPS units. The UPS costs ~$2500? The replacement “packs” will cost a few hundred dollars at least. But the batteries are standard 99.9% of the time, and cost 1/4th the pack if you simply disassemble your existing pack and transfer the hardware onto the new batteries.

I’ve saved hundreds doing this, and since the batteries are standardized, you can usually find a great deal on them beyond their regular price.