Which Battery Actually Starts The Engine? 12V Or Hybrid Battery?

[kofoss]

I have an RX450h 2010 model.

My dealer says that it is the 12V Battery which is the start Battery, i.e. which turns the engine when I start the car.

But I have seen several Lexus owners saying that it is the hybrid Battery which actually turns the engine,

while the 12V´s function is to make the hybrid system ready for the hybrid Battery to kick in.

This is why a small kick-starter is enough when the 12V has gone flat. (Which happens to my car if I leave it unused for 2 weeks, and my dealer says this is to be expected!! My dealer says that I must buy a booster-battery charger which must be connected to the Battery every time I park. If I had known this, I would not have bought a Lexus).

Can anyone tell me what actually goes on during the startup process?

[Gliderpilot]

It's the hybrid batter on my 400h, the 12 volt Battery wouldn't start a relient robin it's so small. According to all that I've read there are three motor generators on the RX, one drives the front wheels, one drived the rear wheels and one is attached to the petrol engine and it's this one that does the starting as you cant hear a starter motor rattle when it kick up.

[Zotto]

The engine is started by HV Battery, always.

You need 12 V to switch on all ECUs, and no need great currents. If you leave your car unused for long time you can keep the 12 V Battery charged with a simple charger with maintaining feature.

[Gliderpilot]

There is a solar panel that plugs into the OBD socket to the top up the 12 v Battery.

[Barry7]

If you refer to my other post regarding the lack of "ready" light, all becomes clear.

Basically, the 12v aux Battery provides initial powering up of the car and makes the high voltage system active for starting and electric drive. What I found when the aux Battery failed was as long as the ignition would come on, power from the high voltage system would give enough power to the aux Battery for the ready light to eventually come on. This was assisted by turning off as many circuits as possible.

I have learnt a lot in the last few days about Hybrid systems, but I still have an awful lot to learn

[Boxbrownie]

Your problem was that you asked your Dealer..............what does he know, apart from levering open wallets :D

[ColinBarber]

Are you talking to a salesman or somebody from service? If service you should consider going elsewhere if they know that little about your vehicle.

[F.A.]

This seems a bit of a flaw of the vehicle if it can not be left standing for two weeks in this day and age. I have read that this is an issue for 400h owners but this is the first I have read from a 450h owner. Very worrying. We have had issues with our Yaris in the past with regards to the Battery prematurely going flat and I worry that a 450h may not be the car for us if this is a common issue

[mbmvw]

Hi

I bought a 2010 RX450h in October, and immediately went abroad for 5 weeks. The car started at once on my return with no hesitation. I was surprised as original 12v Battery was 4yrs old, and I did expect a problem, but all OK. Car was locked normally.

So maybe the 450 does not suffer from the problem 400 car had.

[ColinBarber]

I believe the 450h Battery has a 60 Ah capacity compared to just 38 Ah on the 400h so there shouldn't be the same issue, provided you have a healthy Battery.