# NB2L (Li-Ion) battery intrinsics

Discussion in 'Electronic Basics' started by Agricolus, Jan 23, 2006.

1. ### AgricolusGuest

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.

3. ### AgricolusGuest

Hi Pat.

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

Summarizing: the key link is the following:
http://www.gpbatteries.com.hk/pic/Vcl004.pdf

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 fr.rec.photo.numerique. I will admit
this is true... and report collapse of expensive equipment is it turns
out that it was not... ;-)

Thanks.