NB2L (Li-Ion) battery intrinsics

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.

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I have no idea, but check out

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You may find the info you need at

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Good luck and don't short out any expensive equipment.

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Hi Pat.

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

Summarizing: the key link is the following:

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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... :-) ).
  1. 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... ;-)


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