I’ve got some flat top 18650’s that wouldn’t work in my Ultrafire C8 so I put a big blob of solder on them to make contact. Seems to work just fine and I don’t have to find a small magnet……
Could I be damaging the battery by doing this?
You should be fine doing that as long as you don’t heat up the battery a ton when you apply the blob.
iv’e heard of others doing this…to me I wouldn’t want a magnet that could come loose inside my light and would prefer the solder method…
What kind of magnets are using that fall off metal, lol? Here in the 21st century, most use neodymyium magnets. I had some inch diameter half inch thick ones, that were like a buck a piece, and could hold 32 pounds. When you’d just let two of them smack into eachother they would shatter into dozens of pieces! But you could probably buy some of those little bb sized ones, they’d fit the gap pretty well I’m sure. But, it’s alot cheaper and quicker to just solder on them, and I would trust that a little bit more also. Mainly just because you could get an exact fit if you wanted.
Thanks all! It took a second for the solder to wet to the battery top, but once it did I fed it until it looked like a normal button-top and all was good!
I would rather mod the driver to accept flat tops.. but I've read about adding solder to cells before. Some start by grinding the top a little bit to ensure a better connection (you wouldnt want a cold solder joint to come lose).
>>>>>>What kind of magnets are using that fall off metal, lol?
They don’t fall off, but they migrate and could cause a dead short against the batt compartment wall, which could cause …. Well, it’s not a good thing to short an unprotected 18650 li-ion battery. We all know why.
I did some tests with some small VERY STRONG rare-earth magnets in my lights for this exact purpose. I lightly banged the lights around around for 20-30 minutes (imitating real-life condtions) with a dead 18650, and the mags did migrate eventually so they touched the battery compartment wall. NOT something you’d want to happen with a LIVE 18650. There is nothing on the top of the 18650 in some flat-tops to keep the magnet from sliding around.
After asking here about a remedy, the solder blob was recommended, and so far it has worked GREAT. But previous posters are right. You do NOT want to heat up that battery. So rough up the surface with a little sandaper (or whatever) and make that soldering QUICK, like 2-5 second tops. I haven’t got a cold joint yet by NOT preheating the flat-top top
Best to use a soldering station like a weller where the attached soldering pen has a lot of power behind it, so the item being soldered doesn’t suck all the heat from the pen, lowering it below solder-melt temperature.
ALL IMO anyway. 
Never thought about it shorting out, now I see why you REALLY don’t like magnets for that use. Would it work to just put some tape on the side of the magnet?
I applied epoxy bond on the battery top corners covering the magnet sidewalls. Left it to dry up for a day. So far… So good…