On Fri, Aug 27, 2010 at 9:26 AM, RussellMc wrote: > LiIon is normally known for very good charge retention. > As noted, it may be that protection circuitry impacts this. It seems the batteries concerned may also have been left in the equipment they were powering - in which case there could also have been some standby power draw. Certainly not a good test of the self-discharge characteristics. > LiIon have a VERY =A0approximately linear charge/voltage curve up to > about 60 - 70% of total capacity - at this point they hit the maximum > voltage limit (typically 4.3V for standard LiIon) and voltage and > charge state are less determinate. AFAIR my cells were well up towards > this knee point. Ah, but the _discharge_ characteristics are deterministic (though not so linear) up to full charge. If you were seeing over 4V then they were almost fully charged, as even under no load condiditons LiIon cells drop below this quickly with small amounts of discharge. Of course I'm basing these observations on normal discharge, I'm not so sure that you can assume there is no capacity loss due to self-discharge just because the terminal voltage is still high. > FWIW best storage point for LiIon is just at the constant current / > constant voltage changeover knee. IIRC they suggest about half charge, though I'm fairly sure it's non critical so long as you don't get too near fully charged or fully discharged. Given you can charge LiIon using a variety of different charge currents during the constant current phase, where exactly is this knee point in the absolute charge curve?! > LiIon are actually easier to charge properly than NimH and to know > where you are in the charging cycle. Indeed - you can do a pretty good job using just a regulated bench power supply. Disclaimer - charging LiIon cells can be dangerous, don't do this at home unless you're sure you know what you're doing. Chris --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .