9.85v at the battery plugs when engine's running

Sounds like your voltmeter is bad.

The battery isn't getting charged. So it's either the alternator or the voltage regulator or something else in the charging circuits.

It reads 9.85v while the engine is running because the engine is drawing a few amps to run the ignition, etc.

With the engine off, the battery is reading 11.4v open circuit with no load.

You should read around 14v with the engine running and the alternator charging. And 12+volts at no load.

Andy

Oh, it just occurred to me that you might want to fix this problem. ;-)

First, check to see that the alternator belt is spinning the alternator properly. Make sure it's not loose. Then check the connections from the alternator to the battery to make sure they're not corroded or messed up.

Look for the obvious stuff first.

After that, it starts to cost money.

Andy

I've bought the car 10 days ago and did 600 miles with it. could this be because the battery was fully loaded for the sell ? is it possible for a loaded battery to last so many miles before running empty ?

and thanks for both of your answers.

yomgui

Yes.

A good battery will go 600 highway miles with a dead alternator and minimal electrical load. At lower speeds (more hours) or higher electrical load (headlights, AC, defroster etc.) it will be a lot less.