Why is a 12 volt battery needed in a Toyota Hybrid?
Why not just use the high voltage battery for everything?
In a Toyota Hybrid the 12 volt battery keeps all the electrical system running while your car is parked. This includes the security system, the key fob sensors, the clock, and the memory in many of the computer systems. This is a fairly small drain but it adds up 24 hours a day 7 days a week. The 12 volt battery also has to have enough power to start up the computers and everything else that was left on before the high voltage battery system is turned on.
The reason the high voltage battery is not used for this load when the car is park is that it could easily drain the high voltage battery enough to shorten its life. So if you leave you car parked too long the 12 volt battery gets sacrificed and it is far cheaper to replace than the high voltage battery.
Once the high voltage battery system is turned on a high voltage to 12 volt converter turns on that produces about 14 volts. At this voltage the sealed 12 volt battery charges and will not over charge but it is a slower charge rate than you might be used to.
Now back to replacement: Lead acid batteries come with a chemistry configured to produce lots of cranking amps (not needed in a hybrid because the high voltage battery pack cranks the engine) and deep discharge batteries that produce fewer amps but can be draw down many more times before they fail. The deep discharge type is the better choice in a hybrid because that is all it does. It gets slowly discharged when the car is parked.
I sell Optima deep discharge batteries that I believe will fit in the Lexus and other Toyota hybrid. They are extremely popular with Prius owners. The one I have in my 2001 Prius is 8 years old and I leave the dome light on fairly regularly. (The car starts but I will notice the fixture is hot.) I have a list below of ones that I think will fit (I just need to confirm a few dimension to be sure.) If you are in the Los Angeles area you can come by and I will not charge for the battery installation.
For more information on the Lexus Hybrid click here!
We also have a battery for the Toyota Camry Hybrid (confirmed fit including vent tube connection) Toyota Highlander Hybrid and Toyota Avalon Hybrid .
We have a battery that will fit and even connects up to the vent tube for a Toyota Highlander Hybrid (2011 +, battery in the rear cargo area).
All of these batteries have a vent tube connection that works with the Toyota connector.