Hello:
. l haven't visited since 2012 so all was well until now.

I have the dreaded EL PWR SYS MESSAGE and the red BATT light on the dash of my 2005 Volvo V70.
It has been sitting in the driveway for days at a time due to Covid.
. I checked the alternator and battery terminals. The battery voltage was 12.1 volts-low due to bad battery or not being charged.
. Started car, charge read 13.4 to 13.8 depending on load and engine speed. Disconnected positive terminal and engine continued running.

. My guess is bad battery so I'll probably try that first since there seems to be reasonable output from the alternator.
. Any suggestions would be appreciated.

Thanks, Mike

 

Yes , don't replace parts because you think they are bad.

12.1 static voltage is not a problem, red alternator light generally only comes on if the alternator is not charging (or you have a problem in your DIM) and

You can seriously damage all sorts of very expensive stuff if you disconnect your battery with the engine running - What happens? The battery acts as a capacitor to even out damaging voltage spikes. That test however was safe and valid when cars had generators on them and NO electronics.

You should simply test voltage with a voltmeter and current with an inductive ammeter. Be sure to check again with a hot engine/alternator - worn brushes can charge when cold but lose contact (due to thermal expansion of the case) when hot. The best choice is an alternator tester that actually applies a load to determine the charging capability on the alternator.

 

Good advice above but I must disagree with 12.1 static voltage being "not a problem".

Many a guidebook will tell you that 12.2V is a "failed battery". With marginal voltage such as that you drop down to 10 AND BELOW while cranking.

During this low voltage time (as brief as you might think it is) all the other finicky systems are getting LOW LOW voltage.

How many miles are on your car? My '02 needed an alternator rebuild at 185K (13 years). At that time my friends in the automotive business assured me that my 8 year old battery absolutely needed to be changed too. It cranked the engine just fine but I was told much of what I wrote here.

 

Hello again:

Just an update. My mechanic thought it was the voltage regulator since there seemed to be a reasonable output from the alternator. It was replaced. All is ok for the last month or so.

Thanks for the help.

Cheers, Mike