XXL battery ?

Werner Almesberger werner at openmoko.org
Thu Apr 17 23:39:48 CEST 2008

We had a little discussion about doing intensive data logging,
e.g., to combine location data from GPS, WLAN, and GSM.

For just getting an as comprehensive as possible dump, on which
one can then do data mining, a much larger capacity battery would
be very useful to have.

If we hook a series of bare D cells (to pick the largest easily
available and still pocketable battery type) to the Neo's battery
terminals, we're limited by the PCF50633's maximum battery voltage
of 5.5V (6.5V for the GTA01's PCF50606) and the threshold when our
LDOs lose regulation, which is around 3.6V, a bit less without

With alkaline D cells [1], 20500mAh with a maximum voltage of
1.5V/cell, that would be three cells in GTA02. If we assume that we
draw 200mA (GPS, WLAN, and GSM powered up and passively listening,
backlight off), we'd reach the 1.2V cut-off after about 30 hours.
So that's one set of batteries every 3-4 days, or 900g of extra
trash that's still 66% "full" per week.

With rechargeable NiCad D cells [2], 4400mAh nominal and a maximum
voltage of about 1.35V/cell, we could use four cells. That would put
the cut-off voltage at 0.9V, at which the battery is considered to
be empty anyway. That would give us about 22 hours, until it's back
to the charger. Not too bad, and evironmentally less objectionable
in the long run.

NiMH [3] disappoint a bit with only 2500mAh per cell, which would
give us something like 12.5h.

[1] http://rocky.digikey.com/weblib/Energizer/Web%20Data/EN95.pdf
[2] http://sanyo.wslogic.com/pdf/pdfs/KR-4400D.pdf
[3] http://data.energizer.com/PDFs/NH50-2500.pdf

So far the theory. I wonder if anyone has actually tried such a
setup, and what the experiences are.

- Werner

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