Page 1 of Can you make your own replacement Li-ion battery pack?
This may be slightly niche.
I've got a robot mower. It runs on a little (surprisingly little) battery pack and there's a chance it's starting to fade on me - doesn't run as long, occasional error message. May not need replacing just yet but these things take quite a hammering with multiple daily charges. Anywho, replacement packs for this particular mower don't seem to be available. I was wondering if I just replaced the cells and solder to the controller in the same configuration, I would have a newly replaced (probably considerably cheaper) pack.
Any electronics whizzes have any idea about this? Even pointing me to helpful resources would be good.
The answer is both "it depends" and also "be careful"
It depends on what type the cells are, if they have a protection circuit built in, if you can buy replacements that are the same voltage and at least equal capacity, in the right size. Also, enjoy the fun of getting ones which are not cheap knock-offs that pretend to be one capacity and yet are mysteriously lighter than the ones you took out.
So, say you match all that, the charging/protection circuits are happy with them, you are ready to replace all of them (and they are balanced nicely)...
...you are now in the fun world of soldering tabs of batteries together, and one thing batteries do enjoy doing is getting hot and catching fire. This is where a soldering iron is your enemy, even a quality temperature controlled one. You need a battery spot welder to do it in the safest way, those are fun things!
Mine really loves to trip my house circuit breaker.
You'll find YouTube videos of people soldering battery terminals without problems, and I've even done this myself. But now I would be super careful and avoid it (which is why I bought a spot welder for this purpose, also not a cheap thing). If I absolutely had to do it, I would do it outside, and have a rehearsed method for grabbing a smoking battery and dumping it in a bucket of sand ASAP.
Maybe you'll solder all the batteries just fine! Maybe you'll get unlucky and burn your house down.
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