Alternator bad?

[digger]

when i first start my m20 on a very cold morning the battery voltage is 11.8V at 1000 rpm idle immediately after it has started , when it is warm it is 13.5-13.6V.

is this normal for battery voltage to be low like this? if not what is likely the issue?

i would expect to to be 13.5 to 13.6V always when engine is running

i get that data from my aftermarket ECU by data logging. ive tried to find data from a few years back and ive not found anything that is the same but ive not found identical conditions to compare but one the logs i have it always jumps from about 10.8V cranking to 13.5V when running. never until now has it been 11.8V when actually running that ive seen

battery is 6months old only and cranks well

[dnguyen1963]

What's the voltage w/o the engine running? Have you checked for parasitic drain?

[AndrewBird]

Check the voltage at the battery with a meter to confirm. It shouldn't drop once the car is started, it should rise, so something is definitely up, whether it be an inaccurate measurement, or some kind of draw.

[digger]

is about 12V with ignition on, drops a bit when cranking then goes to 11.8V after its started when its really cold. it doesn't do it all the time usually it starts and goes to 13.5V. i will keep logging it and then check at the battery itself rather than going through the laptop

[JohnH]

Dude, your in Oz, it dosnt drop below 20c. Very cold my arse.