How important is the thermistor in a Li-Ion pack?

[NeoPTLD]

I bought a generic digital camera battery pack from an eBay seller "Bargaincell" The generic battery has higher mAh spec, but it doesn't last anywhere near as long per charge as the OEM battery.

The battery pack type NB-4L has three terminals. +, sense, and -

The OEM battery pack have an NTC thermistor (I think its a 10Kohm)between - and sense. I discovered that the generic replacement I bought doesn't have NTC and its been substituted with a 10kohm dummy resistor. The resistance changes correspondingly to temperature on the OEM battery. The cheapo replacement does not respond to temperature change and remains approx 10kohm.

 

[damonpip]

I believe the main importance of the thermistor is in charging. I think some chargers actually detect when to stop charging depending on the temp of the battery. More likely however, is that the thermistor is there to shut off the charging current if the battery overheats (Li-Ions can explode while charging).

 

[SixEyedSmily]

 

[Mark R]

In a Li battery, the thermistor is for safety. It's slovenly manufacture not to include such a cheap item, but won't affect the operation of the pack.

Most likely is that your new battery has a pitifully small capacity, and the nominal mAh figure is just that (nominal - with no bearing on reality).

 

[MrDudeMan]

Originally posted by: Mark R
In a Li battery, the thermistor is for safety. It's slovenly manufacture not to include such a cheap item, but won't affect the operation of the pack.

Most likely is that your new battery has a pitifully small capacity, and the nominal mAh figure is just that (nominal - with no bearing on reality).

winn4r

 

[pm]

I've noticed that the one NB-4L battery that I bought on Ebay had significantly lower capacity than they had claimed. I have a Li-ion charger than records how much current goes into a battery and is capable of repeated cycling and discharging of the battery recording the amount of current drawn out and put back in again each time (for the curious, it's this Triton charger). I bought an NB-4L for my Canon S500 on Ebay, and it was way off of the 1400mAh described capacity... it was in fact ~750mAh. I wrote to the guys, complained, and they just sent me a new one and let me keep the old one. 750mAh x 2 is greater than 1400mAh, so I was content. I don't have enough positive feedback to want to get into a "feedback war" with the guy, and he did give me what I bought... in the end.

But my net take-away from that experience is that the described capacities of the batteries on Ebay that are substantially above anything else out there are probably not worth the electrons that were used to write the descriptions.

 

[Mday]

lithium ion batteries explode\overheat when overcharged. so do other batteries, but lithium ions especially known to do so.

I dont buy batteries on Ebay anymore considering that I'd rather spend $50 on a battery than $10 on a battery that can damage my $1000+ camera. the only battery i got was for my old cell. worked fine, luckily.

 

[MrDudeMan]

Originally posted by: pm
I've noticed that the one NB-4L battery that I bought on Ebay had significantly lower capacity than they had claimed. I have a Li-ion charger than records how much current goes into a battery and is capable of repeated cycling and discharging of the battery recording the amount of current drawn out and put back in again each time (for the curious, it's this Triton charger). I bought an NB-4L for my Canon S500 on Ebay, and it was way off of the 1400mAh described capacity... it was in fact ~750mAh. I wrote to the guys, complained, and they just sent me a new one and let me keep the old one. 750mAh x 2 is greater than 1400mAh, so I was content. I don't have enough positive feedback to want to get into a "feedback war" with the guy, and he did give me what I bought... in the end.

But my net take-away from that experience is that the described capacities of the batteries on Ebay that are substantially above anything else out there are probably not worth the electrons that were used to write the descriptions.

such an engineer-like thing to say :laugh: :thumbsup:

 

[kpb]

Originally posted by: Mday
lithium ion batteries explode\overheat when overcharged. so do other batteries, but lithium ions especially known to do so.

I dont buy batteries on Ebay anymore considering that I'd rather spend $50 on a battery than $10 on a battery that can damage my $1000+ camera. the only battery i got was for my old cell. worked fine, luckily.

Good point.

Additionally batteries are not part that has an infinite life span. They are a consumable. Just like food a battery does have a shelf life and will go bad. A 2 year old Lithium ion battery will have suffered a noticable loss to it's capacity even if it was never used. I just don't see batteries as a wise purchase off of ebay.

 

[NeoPTLD]

Originally posted by: pm
I've noticed that the one NB-4L battery that I bought on Ebay had significantly lower capacity than they had claimed. I have a Li-ion charger than records how much current goes into a battery and is capable of repeated cycling and discharging of the battery recording the amount of current drawn out and put back in again each time (for the curious, it's this Triton charger). I bought an NB-4L for my Canon S500 on Ebay, and it was way off of the 1400mAh described capacity... it was in fact ~750mAh. I wrote to the guys, complained, and they just sent me a new one and let me keep the old one. 750mAh x 2 is greater than 1400mAh, so I was content. I don't have enough positive feedback to want to get into a "feedback war" with the guy, and he did give me what I bought... in the end.

But my net take-away from that experience is that the described capacities of the batteries on Ebay that are substantially above anything else out there are probably not worth the electrons that were used to write the descriptions.

Do you have a pic of the battery you bought and which eBay user did you buy it from?

Here's a pic of mine:
IMG_0066.JPG
I bought mine form eBay user "bargaincell"