Errmm. The proper way to test a battery is under load. It is possible to see full voltage no load, but have it drop to nothing when loaded. I've seen it personally.

My call on this, from the description, would have been to put the 12 v battery on a charger overnight. Many short trips and long sitting periods without a long trip to charge up the battery will do this, my wife does this occasionally with the same results.

 

In the specifications section of the TCH manual Toyota gives some details on checking the 12 volt battery. The instructions are to check the voltage 20 minutes after the engine is turned off, and all the lights are off. See Specifications attachment. The numbers they give as a guideline are:

12.6-12.8 Volts - Fully charged
12.2-12.4 Volts - Half charged
11.8-12.0 Volts - Discharged

Unlike a conventional vehicle the 12 volt battery in a hybrid does not start the engine. So, there is no drawdown of charge as a result of a start. It just powers up the computers and radio/lights etc. This means short trips should have no affect on the battery charge. It charges off the 245 volt traction battery, and charges all the time the car is in Ready mode. Reving the engine up, unlike a conventional vehicle with an alternator, does not increase the charge. Bottom line is that if your voltage is down 20 minutes after shutting off the vehicle, you have a problem. It also pays to have your own voltmeter to diagnose and replace a battery without going to a dealer. Will cut the replacement cost to about $200 instead of $400.

This said, in a conventional vehicle where the battery actually starts the engine, a current load test is a good one.

6-1 Specifications.pdf

 

One thing that many people don't realize is that there are drains on the 12 v battery after or before the button is pushed to 'boot up' the car. The headlights will stay on for a while, the Air conditioning will start up, the seats need to be adjusted to the driver, and the interior lights will be on while the door or trunk is open. These are all drains, some more significant than others.

Another thing is that the 12 v battery isn't 'instantly' charged up fully when the car goes to Ready mode. Trying to charge a battery too fast is damaging to it, so the charging system is designed to take a while to get it back up to full charge. If your usage is only short trips of a few blocks, then the battery doesn't have time to be fully recharged. Hence the need for a longer trip or a trickle charger.

If the charge on the battery is down enough to fail to boot up the computer, then the car won't go into Ready mode, where the battery will be charged up. You can sometimes turn off the A/C, the Stereo/Nav unit, and the headlights to get the car into Ready mode where it will charge the battery, but you'll need a longer trip (half hour or so) or a night on the trickle charger to get the battery back up to where the problem stops.

Just something to watch out for, and be aware of. It could save someone from buying a new battery when it only needs to be charged up. Even a good battery charger is a LOT less than a new battery at the stealership.