Where to buy a new battery?

It looks like a NiMh pack from the teardown. Don’t mess with that battery unless you genuinely have to - NiMh is a horrible technology compared to LiOn. The other problem with rebuilding it is you need a balanced set of binned cells, which will probably mean buying multiple battery sets and picking the closest match - a little difference is okay as it’s expected (but not much), but you can’t have one cell with 100mAh less power then the others as it’ll run short and the other cells will get negative charge and fail. Forget NiMh exists when you replace it. NiMh is a DUMB technology in the sense all of the pack quality and balancing issues are done with the charger and device owner to properly handle. On the other hand, Lithium is smart and handles all of this.

What works for the Roombas is to search the model and battery online and you can find prebuilt Lithium replacements that drop right in. I would take the model of the vacuum and search that with battery. While you probably can’t buy one from most other countrial due to new battery transport laws, I found a battery on Amazon UK that you may be able to buy. I found that with the model, added battery and put lithium ion at the end. Once you put a lithium battery in, you’ll probably never want to use another NiMh in it.

samsung navibot sr8855 battery lithium ion