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NB2L (Li-Ion) battery intrinsics



Jan 1, 1970
Hi people.

Preparing a trip in a country without electricity, I purchased a series
of NB2L (equivalent) batteries for my Canon 350D. As I'll have more
batteries than needed when I return, I would like to recycle them in
electronics circuits of my design. Something is puzzling me with these
batteries though:
a. These Li-Ion batteries have 3 connectors labelled "+", "T" and "-".
b. The voltage (at full charge) between "+" and "-" is about 8 V
c. The voltage between "+" and "T" is about 6 V
d. The voltage between "T" and "-" is 0V !!!!

I would have expected the voltage measured in d. to be about 2V to
respect the laws of physics... Thus my questions are:
1. How can one explain the fact that voltages look inconsistent ?
2. What could the exact usage of all connectors be (especially the "T")
? (Is it a feature of Li-Ion batteries?)
3. Would it be safe to use only the "+" and "-" in electronic circuits
4. Where I could get a detailed description of the batteries internals
? (Googling a lot, even for the "offical" Canon NB2L batteries, didn't
help much.)

Thanks for any help.


Jan 1, 1970
Hi Pat.

Thanks for the link; it indirectly pointed me to the information I

Summarizing: the key link is the following:

The facts seem to be:
1. The main connectors of the battery are (obviously) "+" and "-".
2. There is an internal thermistor between "T" and "-" (which is likely
used by the charger to avoid overheating). The thermistor is in the 10
kohm range (which I just confirmed with a measurement).
3. The apparent failure of the laws of physics is simply likely due to
the internal resistance of my voltmeter (which must hence be in the
30kohm range... :) ).
4. For electronics applications, only the "+" and "-" connectors should
be considered.

These info seem to be confirmed by a series of postings from Sep 2002
in the French speaking newsgroup I will admit
this is true... and report collapse of expensive equipment is it turns
out that it was not... ;-)