Google has a better memory than me for such things, but from memory,
hard short on data lines indicates a high current source. Memory may
want.

On Apples implementation you can set various voltages on D+ and D-
with resistive dividers to convey charging information.

>From (the same) memory there are some resistor value in the new USB
phone charging spec that allow 'dumb' units to request various
currents.

I would not rely on onboard cell protection circuitry for low voltage
cutoff. This is the worst case level. By setting it somewhat higher
you get very little loss in capacity but sigmificantly extend battery
life. An eg TL431 and a very little glue parts will give you low
voltage protection.

If you are using nipple ended LiIon cells be suer you can tolerate a
non LiIon cell in the battery holder. Alkaline / manganese zince are
easy enough to detect. If you use low current low voltage startup for
low Voltage cells (as you should ) then you can safely insert them and
at worst you will probabl;y just destroy them LiFePO4 is harder to
detect.  (also available in 14500)
Use of tagged cells or of cells wit flat topped end caps and no nipple
- wityh nipple calle being rejected by the holder, will stop some
prob;ems - but not LiFePO4.


       Russell McMahon
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.