CHT gauge in c182p
 

Hi,
As far as I know CHT gauge in cessna 182 with IO 550 works with thermocouple. Some ATPL question banks as well as wikipedia say that it doesnt need external power supply to work. However last time, during alternator's vee belt malfunction when battery voltage got very low I've noticed that cht began to fall down, finally reaching zero. After recharging battery everything came back to proper values.
Could anyone tell me why CHT doesnt work without external battery power?

The CHT could work either way. The original ones do not require a power supply at all, the thermocouple powers the indicator. They will be the indicators which show just one cylinder. However, most modern indicators, and for certain, any with a digital, or otherwise electronic display, will also require power input, which if lost, will result in the CHT indication also being lost. If you would like to understand which type your airplane has, watch it while you turn off the master during your runup, and see if it drops with the loss of power, and you'll know. Also, a read of the POH will tell you what the Cessna configuration is - the system description pages.