battery charger heating up battery

Thread Starter

pager48

Joined Nov 25, 2018
160
after charging a lot of batteries the charger gets warm and its metal battery retaining holder gets warm too.

does the heat which is transferred from a battery charger to the battery while charging it do less or no damage to the battery in contrast to the heat which the battery would generate by powering a load in a circuit?
 

wayneh

Joined Sep 9, 2010
16,102
No, heat is heat. However, the hydrogen formed from overly-aggressive charging can cause an explosion. Charging can also drive off water. Of course that’s referring to lead acid.
 

Yaakov

Joined Jan 27, 2019
1,547
Batteries getting hot for any reason is not good for them but, the reason they get hot is what does the most damage. So, it's really two things. One is the heat, the other is the chemical reaction causing the heat.
 

wayneh

Joined Sep 9, 2010
16,102
Heat is bad for batteries. External heat is probably a less severe problem than heat caused by overcharging, but it’s still bad. What temperature are we talking about? Warm to the touch is probably ok. Too hot to hold is a big problem.
 

Yaakov

Joined Jan 27, 2019
1,547
In this case its mostly heat conducted from the metal charger holder to the battery. Is this just as damaging? cells are NiMh
The upper limit for ambient temperature when charging NiMH cells is 113°F. If the batteries are warmer than that, it’s a problem.

NiMH batteries stay cool for most of the charge cycle, then warm up at the end. That’s normal, but they shouldn’t get hot, that’s bad.
 

oz93666

Joined Sep 7, 2010
669
This is nothing to worry about at all ...

from search ...."The operating temperature range for NiMH cells has been extended to over 100 °C(-30 °C to + 75 °C) which far exceeds the temperature range currently achievable by Lithium cells making NiMH technology ideal for automotive use."

75C is VERY HOT .... what you perceive as 'warm' is about 40C .... at 50C you would not be able to touch the cells without intense burning pain
 

jjw

Joined Dec 24, 2013
502
In this case its mostly heat conducted from the metal charger holder to the battery. Is this just as damaging? cells are NiMh
How do you know, that the heat is coming from the battery holder, not the battery heating the holder?
If the battery is hot to touch, that is not good for the battery.
 

Yaakov

Joined Jan 27, 2019
1,547
This is nothing to worry about at all ...

from search ...."The operating temperature range for NiMH cells has been extended to over 100 °C(-30 °C to + 75 °C) which far exceeds the temperature range currently achievable by Lithium cells making NiMH technology ideal for automotive use."

75C is VERY HOT .... what you perceive as 'warm' is about 40C .... at 50C you would not be able to touch the cells without intense burning pain
The discharge temperature ratings of NiMH and NiCd cells is not the same as their charge ratings. The cells are much more vulnerable to heat while charging and ambient temperatures shouldn’t exceed 45°C. There are also differences among cell designs and not all can handle high temperatures during discharge.

Additionally, staying away fro extremes of hot and cold will extend cell life.
 

Yaakov

Joined Jan 27, 2019
1,547
Measuring batteries currently charging with a IR thermometer Id say I had NiMh batteires 35c-40c. They tend to get hot when they are around 95-99% charged How bad is that temperature?
Getting hot at the end of the charge cycle is expected and normal. Some even use it as the indication of a full charge, though that’s not the best way.

You are probably fretting about nothing. I wouldn’t be worried about it. If you want to maximize cell life, make sure your charger terminates the charge before they get hotter, and remove them as soon after it stops as you can. still, don’t sweat it, your probably cells aren’t.
 

oz93666

Joined Sep 7, 2010
669
The discharge temperature ratings of NiMH and NiCd cells is not the same as their charge ratings. The cells are much more vulnerable to heat while charging and ambient temperatures shouldn’t exceed 45°C. There are also differences among cell designs and not all can handle high temperatures during discharge.
Ambient temp 45C is the air temp , and under high charge /discharge currents , this will equate to a cell temp just less than 75C which is a safe temp for the cell ...

75c is HOT , if you picked up a cell at 60C you would drop it quick ! Too hot to hold !

People are overly anxious when it comes to cell temps due to videos of lithium cells exploding.
 

Yaakov

Joined Jan 27, 2019
1,547
Ambient temp 45C is the air temp , and under high charge /discharge currents , this will equate to a cell temp just less than 75C which is a safe temp for the cell ...

75c is HOT , if you picked up a cell at 60C you would drop it quick ! Too hot to hold !

People are overly anxious when it comes to cell temps due to videos of lithium cells exploding.
I know what ambient temperature is. If the maximum ambient temperature is 45°C, then the cell itself should be raised by contact with another heat source to that or more. In any case, NiMH cells stay at ambient for most of the charge curve and only warm at the end.

And, as I said, operating temperature and charging temperatures are not the same for NiMH and NiCd cells, so your numbers aren’t relevant to this particular discussion.
 
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