"pedro" wrote in message
news
On Wed, 18 Nov 2015 11:59:37 -0800, Jeff Liebermann
wrote:

Yep, and there's a problem. If you charge to 100% and leave it there,
the LiIon battery slowly deteriorates. See Fig 5 at:
http://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries

Yup. The two classical Li-Ion deterioration factors are temp and SOC
- in each case, the higher it is the higher the deterioration.

That's one reason you don't see any LiIon UPS/SPS battery backup power
system. There are plenty of retrofit kits and replacement batteries,
but nothing from the OEM's. Same with cordless phones, electric
shavers, and other devices that run permanently on chargers. About
the only way to do it is to use a battery that's about twice the
calculated capacity ma-hr, and only charge it to 50% of capacity.

When we were doing Li-Ion capacity/cycling testing (in association
with charger design) we tried moving from the cell manufacturer's
"specified terminating voltage for full spec capacity" (4v20) to 4v10.

The critical terminal voltage isn't necessarily a constant.

ISTR: earlier generations of cells requiring 4.10V, most current types like
4.20V - I recently encountered a cell type that should be charged to 4.30V.
The graph on the datasheet indicates useable capacity takes quite a hit if
you only charge it to 4.20V.