I have a feeling I know the answer but wanted some group input. When driving and at idle I get mid to high 13s for voltage but as soon as I turn the engine off my voltage goes to 11.5-11.7v. My battery has a date sticker of 2017 so it isn’t crazy old but it’s some AAA roadside replacement battery that was in the truck when I got it.

So does everyone think that this battery is done and should be replaced? The truck sits for days sometimes and hasn’t had a problem starting but I’ve never seen anything above 11.7v with the key off.

 

I would go ahead and change it out. I'd hate for you to get stranded. it is likely bad, if it's dropping to the mid 11's consistently after shut off.

 

Have you had it tested? Most FLAPS test for free. Likely needs replacing though.

Oh, and get a battery tender on it regularly if it sits for days - this will dramatically extend battery life.