New problem that just started a couple weeks ago. We live in FL and the past few weeks have been colder usual. In the morning, the truck would take a while to turn over. Now over the past 3 days, it's dead in the morning. Today, went to leave in the morning to take the kids to school - dead. Jumped it, turned right over. Wife got back in the truck after dropping the kids off - dead. I meet her, jump it, turns right over, now we are back home.
Once we are home, I leave the truck run and use a DMM to check the alternator voltage. It averaged 14.4 so I'm guessing the alt is OK? Go to leave two hours later - dead. Ok, jump it again, turns over, check voltage, measures around 14.4v again. I left the truck run for 10 minutes, then leave to pick up kids (15 minute drive), leave the truck running at school (5 minutes inside), go back home (15 minutes) and park and let it idle. So for roughly 45 minutes, the alternator has been recharging the battery. While I know this isn't the best way to charge a battery, my charger quit and I didn't have another solution.
Turn the truck off, immediately measure current voltage (engine off), reads around 12.8.
I then gave it 5 minutes, now read 12.6.
I gave it 10 more minutes, read 12.2.
Waited 30 minutes (now 45 minutes from key-off), read 10.6.
Battery is 3 years old. I was going to replace the battery when something else crossed my mind from the past... can a diode be defective? I was going to take the alternator out and have it tested @ Autozone but I read somewhere else that their benchtest may not pickup a faulty diode.
I dont have a problem replacing the battery and/or alternator but I'm trying to narrow down by testing which it is. I have a non-autoranging DMM but my capacity with it is limited.