Car left undriven

Sasbambam · December 9, 2020

Hi Lexus Lovelies.
has anyone had issues with the Battery when the the RX 400h has not been started or Driven for 3-4 weeks ? Is it possible to leave the Battery on trickle charge ? I understand (if I am correct) there are 2 batteries, the electric Battery and a 12v Battery ?. Any advise please ???

NemesisUK · December 9, 2020

One can certainly leave the 12v Battery connected to a trickle charger, such as the CTEK.. One can also use the traction Battery to maintain the 12v Battery as Lexus recommends.

See attached document

Maintainace of hybrid battery.pdf

Herbie · December 9, 2020

38 minutes ago, Sasbambam said:

Hi Lexus Lovelies.
has anyone had issues with the battery when the the RX 400h has not been started or Driven for 3-4 weeks ? Is it possible to leave the battery on trickle charge ? I understand (if I am correct) there are 2 batteries, the electric battery and a 12v battery ?. Any advise please ???

Yes, it's a 'feature' of any hybrid, or at least those from the Toyota/Lexus stables.

The 12V batteries are quite small but that's how the cars are designed and there's nothing wrong or any problem with anything.

A conventional car has a starter motor that will draw more than 300A when it's cranking the engine so the Battery has to be fairly big and beefy to cope with that.

Our hybrids don't have starter motors as such and it only takes less than 20A to boot the computers, pressurise the brakes and get the hybrid system into READY mode, which is the equivalent of a conventional car having been started and just sitting there idling.

This benefits the manufacturers in a couple of ways:

The Battery can be much smaller in both physical size and capacity so there's a cost saving there
Smaller Battery weighs less, which helps keep the overall weight of the car down, which helps to keep emissions down to the ever-lowering limits set by various governments

To us as the owners of an individual car it doesn't make much difference, but when you scale it up to hundreds of thousands of cars, you begin to see the logic in their decision.

The only downside to us is that small batteries will go flat quicker than a larger one would, so we just have to either use the car more or if you don't actually want to move it, Toyota's advice during the lockdown is to have it in READY mode and 'Park' for about 60 minutes per week while you sit in it reading the paper or whatever.

As I said above this is the way the cars are designed, so quite a few of us on here carry one of these jump start Battery packs or something similar in the car 'just in case' and they're well worth it for the peace of mind alone - they really do work superbly well. I decided to make a 'comfort' jump start point in the cabin so that if the weather was bad when I needed to do it, at least I'd be dry - details below if you want to fit one to your car:

Barry14UK · December 9, 2020

If the 12v service Battery is under bonnet, as was the case with some earlier cars the size is probably larger than in later cars like the RX450h which have it in the boot. If it's in the boot (nearside rear), it has only a small capacity and should ideally be charged every two or three weeks, either by running up the car, using a regulated solar charger or smart charger with max 5amp charge. If this special AGM battery is new it will last longer before needing a charge but when say 5+ years it may need to be charged more frequently. This Battery powers computers, clock, and alarm etc., and initiates the high voltage traction Battery. You don't want to let the service Battery go flat as it can cause problems and shorten the life of the Battery. If the Battery is under the bonnet things are not quite so difficult but it will still need to be charged in order to initiate computers to connect the traction Battery. The high voltage traction Battery will go for several months and is an expensive item to replace or have rebuilt. You can't charge it yourself other than by driving. It is therefore worth having this traction Battery checked by Lexus annually who will guarantee it for a further year if it meets certain criteria.