lexus rx400h - auxillery battery failure

Honest John Back Room » Technical matters
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Fri 15 Oct 2010 15:57
lexus rx400h - auxillery battery failure - selexus

i am about to leave my lexus rx400h at an airport for 2 weeks and i am told that it is commonplace to return and find the battery flat.i gather that the auxillery battery is only small but with the amount of "kit" on these cars the battery flattens quickly.i am also told that there is no bigger replacement battery that will fit this model.can you offer any advice.the dealers dont seem to be able to help and the lexus owners club correspondence indicates that lexus dont want to know.one of the reasons i bought the car was because of the rave reviews by "honest john"incidentally i agree with his views on the car but i see this as a really annoying potential drawback to the car.

Reply | Report as offensive | Link
Fri 15 Oct 2010 16:39
lexus rx400h - auxillery battery failure - Collos25

I personally think your car will be ok the worst is you will need a jump start but having left a variety of cars far longer than you on return they have always started when required ,they make a solar charger that fits into the cigar lighter socket not to expensive and will achieve what you require there are hundreds available on ebay.

Edited by Andy Bairsto on 15/10/2010 at 16:42

Reply | Report as offensive | Link
Fri 15 Oct 2010 19:54
lexus rx400h - auxillery battery failure - Peter.N.

...or just disconnect the battery while its parked

Reply | Report as offensive | Link
Fri 15 Oct 2010 19:57
lexus rx400h - auxillery battery failure - Collos25

Not a good idea on a lexus.

Reply | Report as offensive | Link
Sat 16 Oct 2010 00:14
lexus rx400h - auxillery battery failure - Peter.N.

What's the difference between that and it going flat?

Reply | Report as offensive | Link
Sat 16 Oct 2010 11:14
lexus rx400h - auxillery battery failure - Collos25

If you do not know that then you should not be giving advice and telling people to disconnect the battery.

Reply | Report as offensive | Link
Sat 16 Oct 2010 11:20
lexus rx400h - auxillery battery failure - Peter D

What do you mean "Auxillery Battery" Do you mean the main battery.

Regards Peter

Reply | Report as offensive | Link
Sat 16 Oct 2010 14:33
lexus rx400h - auxillery battery failure - Peter.N.

Mr Bairsto, I don't pretend to know everything about cars and try to only give advice on things that I have personally experienced, I was however an electronics engineer all my working life and cannot see the difference between a flat battery -0 volts and a disconnected battery- 0 volts and would be pleased if you would enlighten me.

Reply | Report as offensive | Link
Sat 16 Oct 2010 17:24
lexus rx400h - auxillery battery failure - Collos25

Because a battery will never go to 0 volts in such a short time it will keep enough charge to keep the alarm ,clock radio,ecu etc working disconnecting it will make these and anything else that requires a constant voltage so as to require reseting and if I remember correctly if you just diconnect the battery on this vehicle it can cause all sorts of problems.I can just see someone pulling up at the airport carpark ready for their holidays going through all the problems of disconnecting the battery and when they return on a wet dark cold night trying to reconnect it and get everything to work why go through all this when there is a perfectly good cheap solution.

A car battery left for a very long time might not have enough power to start the car because it will require a large amount of availble amperes but it will still produce 10/13 volts and will produce enough amperes to keep ancillary equipment running.Thats providing the battery is in good health.

Reply | Report as offensive | Link
Sat 16 Oct 2010 19:17
lexus rx400h - auxillery battery failure - kithmo

Easiest solution is to buy one of those portable jump starters and leave it in the boot.

Reply | Report as offensive | Link
Sat 16 Oct 2010 23:29
lexus rx400h - auxillery battery failure - Peter.N.

I take your point, I was looking at it from the point of view of a completely flat battery, would the voltage not drop to near zero if you tried to engage the starter, or does it have circuitry to prevent the starter engaging below a certain voltage?

Reply | Report as offensive | Link
Sat 16 Oct 2010 19:56
lexus rx400h - auxillery battery failure - Roly93

Not a good idea on a lexus.

Notg a good idea on most hi-tec modern cars especially something as technology packed as a Lexus. There can be all sorts of system and security issues if you do this.

I rgularly leave cars for longer than this and there is never a problem, I think you are worrying unneccesarily, that is unless you thing your battery is on the way out ???

Reply | Report as offensive | Link
Sun 17 Oct 2010 10:15
lexus rx400h - auxillery battery failure - elekie&a/c doctor

I am fairly sure that a flat aux battery is not a problem ,as the car will run on the electric motors from main battery or fire up the petrol engine via the E -motor.There is no starter motor or alternator fitted to this car.hth

Reply | Report as offensive | Link
Sun 17 Oct 2010 21:42
lexus rx400h - auxillery battery failure - priusdriver
If the 400h is like the Prius, then the aux battery is only there to run the accessories with the power off, and energize the relay to the traction battery when you power on.
If the aux battery runs flat (as happened to me once), you just need to put a 12v supply across it to energise the relay. You may then need to re-train the power windows!
Reply | Report as offensive | Link
Wed 12 Dec 2018 17:21
lexus rx400h - auxillery battery failure - Writer
Re the hybrid battery problem, you mentioned having to retrain the window s?

How does one do such a thing?

Thanks

Nick H
Reply | Report as offensive | Link
Wed 12 Dec 2018 21:56
lexus rx400h - auxillery battery failure - Oli rag
I doubt you will get an answer from that person as the post is 8 years old.

Not sure on a Lexus, however the normal method for resetting electric windows is to hold the control switches up for 10 seconds or so.
Reply | Report as offensive | Link
Thu 13 Dec 2018 08:23
lexus rx400h - auxillery battery failure - elekie&a/c doctor

The only difference on lexus models ,is that the auto window re-learn sequence has to be carried out from each switch of the corresponding door .It cannot be done from the driver door master control switch.

Reply | Report as offensive | Link
Thu 13 Dec 2018 10:52
lexus rx400h - auxillery battery failure - Hugh Watt

Eight years on, but elekie&ac doc is still there to help! I think his contributions here are much appreciated.

Reply | Report as offensive | Link
Mon 17 Dec 2018 23:12
lexus rx400h - auxillery battery failure - SteveLee

The only difference on lexus models ,is that the auto window re-learn sequence has to be carried out from each switch of the corresponding door .It cannot be done from the driver door master control switch.

Spot on, you'll also notice the individual door switch illumination will flash indicating the windows need resetting.

The first sign your auxiliary battery is weak is often refusal to go into "ready mode" with a warning telling you to shift to "P" even though the car is already in "P". There is a Bosch S4 battery with slightly higher rating but it's so expensive it's not worth the premium. Keep one of those little cheap mobile phone sized jump packs in your glove-box, they will usually provide enough of a boost to get the car started if your auxiliary battery is weak, it's the traction battery that actually turns the engine over.

Reply | Report as offensive | Link