12v Battery - Voltage Variation between Posts and Diagnostic Screen

I had the same problem recently and found I needed a new battery in the multimete. With a new battery in the meter readings fell int a normal range.

 

Put the car in ready mode get out and go back and measure across the positive and negative terminal again what do you have? Should be like 13.7 to 14.5 somewhere in there. Sitting 8 hours and showing 16 volts on the battery I'm wondering if your multimeter or testing instrument needs a battery or there's something wrong with it 3 volts overcharge does not do good. Take your multimeter to another 12 volt battery maybe one that's sitting in a friend's car or something and measure across its positive and negative terminal If you're still getting 16 volts I would say there's something wrong with your meter I don't know of any car that's going to charge the battery to 16 volts regulators and everything stop happening now it is possible that the charging circuit from the HV battery has gone amiss but usually it would undercharge I wouldn't think it would over that battery should be getting warm you should be smelling battery in the back of your car. Yes that battery may be original or by the looks of the car it's probably been maintained at the Toyota dealer a quick scan of your cars VIN . May tell you who maintained it Good luck

 

I don't trust that multimeter as far as I could throw it. 12 volt batteries just don't show that kind of resting voltage. As another poster has suggested, maybe the multimeter's own battery could use replacement.

My experience with the vehicle signal check screen is it tends to read half a volt or so lower than you would see at the battery posts. So I would take that as a reading a bit below 12 at the posts, well short of fully charged, so giving that battery a good long visit with a charger might not be a bad thing.

 

it might be under the strap, but there should be a date code.

might be the original battery, idk if you could ever buy a replacement toyota, they are usually tru start at the dealer.
both made by yuasa, iirc.