Originally Posted by Ron AKA (Post 242610)

The 2012 Owners Manual says the following about the 12V battery in the specifications:

12.6 -12.8 V Fully charged
12.2 -12.4 V Half charged
11.8 -12.0 V Discharged
(*: Voltage checked 20 minutes after the engine and all the lights are turned off, at 68 deg. F)

It would seem to me if you were consistently getting Half Charged range when you test with a multimeter, I would start to get concerned. If you then check voltage when the car is running and hopefully charging, I would expect it to be up around 14-14.5 volts. If it does not come up to that, then you can suspect the charging system.

Another way to evaluate the state of a lead acid battery if it has removable cell caps is to measure the specific gravity with a battery hydrometer. They are relatively cheap. If you have a suspect battery, you can confirm it by testing each cell to see how uniform they are. Often you will find one cell is lower than the rest. The only trick of this test is making sure you don't get any acid on your car, hands, or clothes!

On buying a replacement, cranking amps or CCA is irrelevant as this battery is not used for starting. Buying a deep cycle seems to make a bit of sense as there does seem to be a drain on these batteries when the car is not running. Generally you can tell the capacity of a battery for deep cycle by the amp-hour rating, or the reserve minutes. More is better.

Consumer Reports I recall used to test Optima and recommend them, but in the latest tests they do not seem to be included. DieHard Gold and Platinum seems to test near the top in most sizes.

Does the original battery have a vent connection? Venting of the hydrogen and oxygen would seem to be a bit of a concern as it is located in the trunk rather than under the hood where there is lots of ventilation.

Originally Posted by mt1221 (Post 272171)

You have no idea what you are talking about. The 12v battery in ALL Toyota hybrids STARTS THE ENGINE. Only AFTER the vehicle is in a "running state" does it rely on the hybrids battery pack.