How Do I Know If My 12V Battery is Not Charging.

document the dead battery and have them replace / recharge it again, and see if they do it right this time.

 

put a volt meter on it with the car ready, it should read around 14 volts.

the other possibility is that you have a phantom drain while the car is off.

or you are simply not driving it enough to keep it charged, because there is always a small drain when it is off.

 

You can get OBD meters; either a hardwired solution (Scanguage II) or a wireless OBD device that bluetooth's (yeah that's a verb, LOL) to your phone. TON's more info besides a voltmeter in these solutions that you can appreciate like the HV battery health.

 

^ This.

I think the dash display can also show battery volts, with the car fully on (aka "Ready" in Toyota speak). Never done that myself, maybe not possible on our model (no touch screen).

 

Prof. John Kelly of Weber University has a video that shows how you could verify whether or not your charging system is working properly. Another option is an inexpensive battery tester (ToPDon BT100 works well) that can test your battery, the charging system, perform a cranking test, even track the Internal Resistance, allowing you to anticipate future performance.
You can even simply hook it up to your battery and check the voltage without having to turn it on. Very simple to use and will give you significantly more info than a simple voltmeter.

 

I seem to remember long ago discussions in which that as a Gen2 thing, not Gen3. But since the OP has a Gen2 ...

I use my old trusty ScanGauge-II, but there are plenty of newer / better / cheaper OBDII-port engine monitors that will show it, continuously if desired.

 

Gen 3 cars with the touchscreen have the Vehicle Signal Check screen where you can see the 12 V voltage (typically half a volt or so lower than you'd see elsewhere in the car). The Gen 3 cars with just the couple-line LCD radio displays, I think, don't.

 

I remember having an ammeter in our cars, right alongside an oil pressure gauge to supplement, as they were called by some engineers , "the two idiot lights on the dash"
They weren't supplied by the cars manufacturer though.
It's be interesting to find out what cars came with an ammeter standard.

 

I had that two-line LCD version for three years, before upgrading to the current car, so my memory is somewhat stuck on that first version.

 

The two-line LCD versions do offer the same infotainment DTC information that people keep discovering on the touchscreen versions and mistaking for car DTCs.

But, happily, the UI for retrieving them in the 2-line LCD version is so punishingly awful that probably people won't be stumbling on them as much.

 

I trying hard to be over critical here, but how exactly are these posts helping the OP to understand their situation?

 

There is a resource for a significant amount of information about batteries called (believe it or not) The Battery University. The information you could find there will help you, and help weed out the “PriusChat” nonsense.
As far as your original question goes it boils down to:
1) The battery itself is bad or failing (you can have it tested at nearly any repair shop or parts store for free, or buy one and test it yourself).
2) The charging system is faulty (again, easily tested (see my original post).
3) You are either leaving the car in ready mode or leaving a light or a door open. In short, drawing down the battery.

Basically it is like any other car: if the battery is dying it is going to be from one of 3 causes: bad battery, bad charging system, something being left on. I truly hope this helps.

 

Using the built-in dashboard voltmeter can tell him whether or not the charging system is working, without having to acquire other tools.

 

I will trust you on that as I have no experience with it. It boils down to “is the battery good, battery being charged, battery being drained”. Answer those questions and solve the mystery.