Now that electronic cigarettes have reached the point where you can buy a complete disposable one in pound shops (dollar stores) it's interesting to note that despite being "disposable" they may actually have a rechargeable lithium cell in them due to the sheer mass production of rechargeable cells making them available cheaply in a huge range of sizes. I decided to put this to the test and removed a cell from an e-cig. They don't have any built in protection circuit against overcharging and discharging (that bit's normally built into the e-cig control circuit) so I used the protection board out of another cell to build a module that allowed me to charge and test the cell. I ran a cautious charge cycle, monitoring the cell for swelling, temperature increase or venting (I put it in a non flammable container!) and it took a full charge in about an hour at 100mA. I then plugged a load onto the protection circuits output and it supplied about 100mA for an hour before the protection circuit kicked in. I then repeated this for several charge-discharge cycles and the cell does seem to be a fully rechargeable cell.
Obviously I can't guarantee this between different brands, but so far the EZI-cigs do seem to contain a 75400 (7.5mm diameter by 40mm long) 90mAh rechargeable lithium cell.
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