On Tue, Sep 27, 2011 at 6:09 AM, RussellMc wrote: > > #1 What factors limit the lifetime of Lithium batteries ? > > Cycle life. > > Battery mechanical structure changes as storage is depleted of Lithium > metal and battery mechanically flexes itself to death. 300 cycles > often claimed. Some brave souls say 500. Not going to very top on > charge helps. LiFePO4 gets 2000+ cycles by having a structure whose > size/stability is not dependant on amount of li metal in store at any > time. Cost is lower capacity. > > 18650 LiIon get 2000 - 2500 mAh. High end can be suspect. Some claim > 3000 mAh +. Walk carefully away with hands in sight. LiFePO4 is about > 1200 mAh. > > Calendar life. > > Cell starts to electrochemically degrade from 1st use. Lofe unknown > and will vary but maybe 3 years. > LiFePO4 not known to have a calendar life limit. It may hav but I've > never seen it mentioned. > > > #2 What is the #1 factor limiting energy storage ? > > Amount if Li metal that can be effectively crammed into space without > getting very short lifetime. > LiFePO4 is a better bet $ wise if absolute energy densities are not > a major issue. > > Surprisingly, modern NimH energy density is about as good as many LiIon. > > LiPo =3D Lithium polymer are variants on LiIon theme and probably > similar life etc. > YMMV. > Very good stats. 300 cycles is interesting. I'm assuming that's full charge to 4.2 volts and "fully" deplete to the minimum safe voltage for Li-ion. Ho= w much do the stats increase by only charging to 4.0V and only cycling betwee= n approx 30-90% SOC? Assuming 90% SOC is the upper limit by charging somewher= e between 4.0-4.1V. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .