To see if it is the Battery check the Voltage before you shut off the Engine. If it is good; turn the Engine off and diesconnect the Negative Battery Cable.

If the next day the Batter Voltage is low you know it is the Battery causing the voltage drop.

I am not picking on you on this but I have always been curious about this. I have read a lot of these threads where it may or may not be the Battery causing the issue.

Since People usually have more than one Vehicle or have a Friend with a Vehicle why they do not substitute another Battery from another Vehicle just for test purposes.

__________________
84 300D, 82 Volvo 244Gl Diesel

you know, i'm pretty smart about stuff like this but i didn't even think about disconnecting the battery overnight. great idea.

__________________
1981 NA 300D 310k miles

I had something draining My Battery overnight on the Volvo Diesel. I installed one of thos Harbor Freight manual Battery Disconnect Switches that mounts on one of the Battery Terminals.

For a year I had to open the Hood and turn the thing one when I wanted to drive and off when I thought the Car was going to sit for several hours.

I located the Battery driain by accident when I had the Drivers Door Panal off to change the Door Handel.
The insulation was gone from part of the Wires going to the Door Lock Actuator. You could see the sparks when you moved the Wires around.

Attached Thumbnails

 

__________________
84 300D, 82 Volvo 244Gl Diesel

ok, tested immediately after shutdown: 12.4V
battery disconnected, 14 hours later: 12.17V
0 amp draw with everything off

__________________
1981 NA 300D 310k miles

There is a surface charge on a battery that has just stopped charging. So the overall drop off overnight is not conclusive. What is troublesome is the low voltage at disconnect.

Are you sure you cannot turn your alternator pulley by the fan blades on the alternator pulley? You may be getting adaquate voltage but not enough current delivery from the alternator to charge that battery properly. I do not think anything is clear enough yet to say it is the alternator or battery.

can't turn the alternator by hand. a couple weeks ago when this started to get worse i tightened the belt. the alternator has been making a chirping noise for a long time (2 years). i thought maybe it was just the belt, but it persists. so maybe theres a worn bearing, but it checked out OK for output.

yet again i tested, four hours after shutdown i have 12.10V. i'll check again in the morning.

__________________
1981 NA 300D 310k miles

forgot to top this in case others have the same problem. i replaced the battery a month ago with a duralast gold from autozone and have had no problems since.

__________________
1981 NA 300D 310k miles