18 July 2017

32600 Li-Ion batteries

Not much is going on this Summer 2017: it is just too hot! Meanwhile a friend gave me a couple of battery packs from a burglar alarm system. They get replaced yearly during periodic service. The label states Li-ion, 2x 3.6 V 13 Ah. Pretty little beast: it can almost direct-drive a bunch of while LEDs and make a lot of light, or last very long. But all contacts measured 0 V, or open circuit. Time to... pry it open!

I was expecting to see some 1SxP configuration and instead I found two 32600 cells. They are huge, like D batteries. Also they are not connected in parallel.

I recall that some Li-Ion batteries have an embedded protection circuit from over-(dis)charging, that disconnects the battery (= open circuit, or 0 V) when it is too low. In fact once I fed some 4V to each cell it sprang to life and started charging.
32600 vs AA

Unfortunately there do not seem to be cheap flashlights that can host this cell size (32600 or the more common and slightly longer 32650), so I will have to build mine. If this cell has a capacity close to 6000 mAh, I can run a 1W while LED for about 15 hours, or a normal 5 mm LED for 300 to 600 hours! Or a booster to 5V makes it a bulky powerbank.

Well, I spoke too soon. Since it already happened to me that a Li-Ion element started self-discharging and self-heating, I was periodically checking voltage under charge and no-load as well as temperature (to the touch). It went like this. Both elements stabilised at 3.96V. When I removed the charging source the voltage dropped steadily down to 3.60V,  about -1 mV/s. At 3.6 V thereabout they heated up, warm to the touch. Voltage stable. After one hour they were ambient temperature and reading 0 V again.

I will not bother with the second pack and bring them both to the recycling center.