[ehnto]

I always double check battery replacements before buying items for this reason. It is hard to predict what sizes will stick around, but I am also not against busting a device open and fitting a near-enough sized cell with the right output.

[Lio]

18650 cells seem to be a good standard for things like torches and bike lights.

As a plus you can pick them up in e-cigarette shops, apparently vape units use them too.

[soylentcola]

The ones for vaporizers (and flashlights) may be overkill. They tend to cost extra because they're "high drain" batteries meant to be safely discharged at a rate higher than most electronics. Depending on the use, you can get much less expensive 18650s than the ones used for vapes.

Often you can get them with leads/connector pre-soldered (which is good for hobby electronics since you don't really want to be soldering straight to a lithium battery and not all electronics already have a cradle)

[peshooo]

I have a cheap-ish bike light with 18650 battery. After it stopped working, I tried to replace it, but I couldn't solder it so well like the factory one. The mtb rides shake a lot, so my solder joints break.

Any hints how to solder it better?

[ehnto]

In motorsport wiring they use crimped connections instead, due to it's mechanical strength compared to solder. It withstands the vibrations and movement better. You can get really small crimps so you should be able to find some that fit. If it's soldered to the PCB I haven't got much advice sorry. One option might be to mechanically support the wires near the solder, maybe hot glue the battery or wires in place so they can't pull on the solder.

[smileypete]

Solder will wick up the wire and create a 'hard spot' where it breaks upon the wire flexing. Try using a blob of hot melt/sugru(sp?) around the wire in this area, to create strain relief.

Another tip is to use plumbers flux and an old soldering bit to 'tin' the battery first, the solder will fairly leap onto it with such flux. :) Don't forget to clean the flux residue off as it's quite corrosive.

[alias_neo]

They do. I vaped for a while, and my wife bought a battery powered fan for when she went into labour and it came with some cheap 18650. Luckily I had a few high quality Samsung ones lying around from my vaping days that came in handy!