My wife buys these cheap disposable e-cigarettes:
You're supposed to toss them when they're dead, but I know for a fact these use lithium rechargeable batteries, or else they wouldn't be able to supply the right voltage and current to last "800 puffs". There’s no disposable alkaline battery on the market that I’m aware of that would come in this size and last as long. A watch battery would be dead in an hour. These things last days.
I asked her to give me the next one that dies so I can take it apart. I cracked it open to see what was inside.
Wouldn't you know it... a 1300mW LiPo battery! Well, it’s looks “LiPo”.
It measures 3.3 Volts. Yeh, definitely LiPo. So it’s not that the battery on this one died, it’s just that it ran out of flavor.
In order to see if I can recharge it, I wanted to kill the battery first. I hooked it up to a coupe of LEDs, but after 20 minutes, the charge was still the same.
Time to ramp things up. I connected my RGB Night Light and my Mini 7-Segment Clock to it. That's 2 microcontrollers, one DS3231 and ~50 LEDs. That should kill it!
It took a good 20 to 30 minutes before things started dropping out. I measured the voltage and it was still 2.7 volts.
I connected it to my SparkFun LiPo battery charger and let it sit.
I kept an eye on it for about an hour to make sure it wasn’t gong to catch on fire or meltdown. It wasn’t getting warm, so I left it alone. About an hour later, the charge indicator turned off. Did it charge? Or did it just give up?
I connected my meter and voilà! It reads 4.17 Volts. It worked!
Looks like I just found a cheap source of really small, but powerful, LiPo batteries! They’ll definitely come in handy for shrinking down projects. I can only imagine what they’d cost buying them on their own, but if you can pull one from an $8 e-cig that you’re using anyway, then the more the merrier.