Laptops run hotter when battery is being used?

[thinkpadlover]

Earlier I posted about my Lenovo ThinkPad R61i 8932H2U. Intel Core 2 Duo at 2 GHz. I replaced the fan assembly myself with a refurbished one. With 100% load on the processor, temps were peaking at around 83 degrees Celsius... but that is with the battery installed (and either straight off the battery or plugged in with the battery charging).

The battery is out and I'm plugged in only. 100% load -- peaking at only 42 degrees Celsius!

Is this the way laptops are? Run quite a bit hotter with the battery installed? Maybe because the fan runs slower on battery power?

 

[dodger46]

Don't know about Lenovos, but my HPs runs at a lower power setting when on battery to conserve it, and hence run cooler!

 

[das_stig]

Could be a bad charging circuit overcharging the battery.

 

[kitsunestarwind]

There will be heat generated by the battery charging and discharging.
More then like though its related to power modes. on battery power most fans are set to only cool when a set temp it reached. on AC most fans are set to stay on all the time

 

[thinkpadlover]

I don't think it's a bad charging circuit -- everything seems to check out fine with the battery and it charges in the expected amount of time. Also, I don't think it's the power mode -- both battery and AC settings are on Maximum Performance. I think it's just the additional heat from the battery charging and discharging. Also, I think it might be because when the battery is attached, it's harder for the heat sinks and fan to dissipate heat because you have this already warm block right next to one area of the fan assembly. Not sure. Just a theory.