Flat Battery On Rx450H

Arty1943 · January 23, 2015

I have left my 2009 model RX450H unattended for 3 weeks and will expect to find the 12V Battery flat when I return to it. If the Battery is flat how do I unlock and open the tailgate to access the 12V Battery in the boot area for re-charging or jump starting the car? Also if I start the car and want to run the engine to boost the 12V Battery charge, or demist the front windscreen before driving off, do I need to select the Neutral gear or will it run whilst still in park?

Please help!

Regards Richard.

Pooh-Bear · January 23, 2015

There is a 'jump start' terminal under the bonnet to use. It is detailed on page 582 of the owners manual and tells you how to go about 'jump starting' your car.

Arty1943 · January 23, 2015

Is that the terminal that you can also use to Trickle charge the Battery? (for my future use/reference)

Pooh-Bear · January 23, 2015

It seems to indicate that in the manual (if you want to trickle charge it without removing the battery). Once recharged the power back door (if fitted) needs to be re-initialised details on Page 617. And, if you have trouble starting once recharged page 482 gives tips on sorting this out too!

stevet · January 23, 2015

Why do you expect it to be flat?

DanD · January 23, 2015

I thought the Battery problem only affected some RX400h, and was resolved with the RX450h.

In all cases, whether it is the 400 or 450, you must leave the car in READY mode, and the gearbox in Park in order to run climate control, demister, radio etc. In Park, the petrol engine will kick in automatically to top up the Battery. This will not happen if you leave the gearbox in Neutral. You will find confirmation of this - and probably a better explanation than mine in the owner's manual.

Arty1943 · January 23, 2015

Thank you folks for your interest and response to my questions. Hopefully my concerns will not be realised when I return home, but at least I now know how to solve them if they occur.

Regards

Richard.

ColinBarber · January 23, 2015

I thought the battery problem only affected some RX400h, and was resolved with the RX450h.

The 450h is better but if your Battery is long in the tooth and lost some of its capacity then it won't last as long as it once did.

Normal advise from Lexus/Toyota is to disconnect a Battery from the vehicle's electrics before charging, even just a trickle charge. Personally I don't bother but if possible I'd connect directly to the Battery rather than using the remote contacts for charging - if it is a true trickle charge then I don't see an issue using the remote contacts.

regrim · January 29, 2015

I Have heard this before I own a Rx450H also a Saab if I leave the saab for more than 3 weeks Battery goes Flat I purchased a Solar panel that trickle charges at 4amps and plugs into OBD!! socket Brilliant no more flat batteries £40 from amazon!

nelmo · February 8, 2015

Wowsers, when the Battery lets go, it lets go!

About 3 weeks ago, the car refused to start so had to get a jump start from a neighbour. All fine until yesterday, when the car wouldn't start again. Jump started again and then left it on trickle charge overnight, expecting it to be ok in the morning BUT no, still dead as a doornail!

I guess this really cold weather hit it hard and it was already on its last legs...got a new one today so hopefully will be ok for a while now.

regrim · February 8, 2015

Hi New Tip I have just learnt A Battery I bought a year ago off eBay with 4 years warranty was flat has a dodo last week I put it on charge overnight I have a sealey 10amp charger next morning still nothing, I Tel supplier who asked me to try this first Jump Battery for 20 mins from a good Battery then put charger on, It worked and fully charged Battery!

Apparently these super duper new chargers need to read a voltage to operate - No Voltage No Charge - found when I connected Battery the boot light had discharged, Learn something new everyday and the company saved a replacement!

CanJIm · April 17, 2020

Can I use a trickle charger to maintain power in the car while I change my Battery?

ColinBarber · April 17, 2020

5 minutes ago, CanJIm said:

Can I use a trickle charger to maintain power in the car while I change my battery?

Not something a trickle charger, or any charger, is designed for and therefore I should say you shouldn't do it, but I also know it will work. Just make sure you don't make a demand on the Battery by opening the doors or letting the auto lights come on etc.

If it is an intelligent charger then it may not work, as if it detects no Battery it could automatically shut off.

malcolmw · April 17, 2020

Be very careful with this. The Battery acts as a smoothing device (like a capacitor) and suppresses voltage spikes and surges on the vehicle system. Using a smart charger may result in shut off as described earlier. Much better to use a jump start Battery pack as the bridging source.

Herbie · April 17, 2020

Exactly what Colin says, but just to add that you can basically use almost any 12V source just to keep the settings while you change the Battery.

When you park the car up for the night it may take a couple of hours for it to 'go to sleep' as it were, but when it does there will be a quiescent current drain of somewhere in the region of 36mA to 50mA being supplied by the Battery to power the alarm, the radio presets and maybe other stuff too.

Given that you want to change the Battery you'll have the tailgate open at the very least, which would switch the interior lights on. As long as you manually switch them off (because they would probably be the biggest current drain), you could even use a Battery pack with 8 AA alkaline batteries like the one pictured below and that would happily keep all settings alive while you change the car Battery, with plenty of current to spare (typical AA Alkaline batteries rated at 2800mA) - but better to do it quickly 'just in case' :laughing:

CanJIm · May 8, 2020

I bought a solar Battery keeper and I have it connected to the data terminal under the steering wheel. Does anyone know if the data terminal is live when the car is off and locked?

Illogan · May 8, 2020

You're referring to the OBD(2) socket

- and yes - I have connected my solar panel to that socket to trickle charge the 12v Battery

CanJIm · May 9, 2020

Yes, the OBD11 socket under the dash. Thanks for the reply, good to know, a relief. My Battery has been giving me problems as the car doesn't get driven much during the pandemic lockdown. This should really help.

Tony L · June 7, 2020

Also had completely flat Battery on my 2012 450h during lockdown and now considering solar trickle charger.
How should I connect it to the OBD2? Is that the best place?

Illogan · June 7, 2020

5 hours ago, Tony L said:

Also had completely flat battery on my 2012 450h during lockdown and now considering solar trickle charger.
How should I connect it to the OBD2? Is that the best place?

As you'll note from a comment I made earlier - the OBD2 port is an excellent point to plug in a solar trickle charger.

Just be aware, of course, that if your Battery is totally flat then it will take some considerable time* (as in days) of reasonable sunshine for a Battery to be charged purely from a small solar trickle charger.

* (Battery science is wonderfully complicated, and I have grossly simplified it with the above statement)

(as an aside: - - -

My Battery was similarly flat a couple of months ago (before I got a solar panel) but I was able to use my NOCO Boost HD GB70 (jump start pack) to start the car, and give it a decent run before I relied on the solar trickle charger, but it has been as 'good as gold' since.

Mesh81 · March 12, 2021

I'm having the same problem in that hardly used the car over lockdown, and now the Battery is flat, have purchased a NOCO Boost HD GB70. Thanks for that recommendation. Can you recommend a solar trickle charger to help keep the Battery topped-up.

Illogan · March 12, 2021

1 hour ago, Mesh81 said:

I'm having the same problem in that hardly used the car over lockdown, and now the battery is flat, have purchased a NOCO Boost HD GB70. Thanks for that recommendation. Can you recommend a solar trickle charger to help keep the battery topped-up.

Hi Umesh

This is similar to the item I bought https://www.ebay.co.uk/p/26031190058

(It's available from many outlets, not just Ebay)

But please be aware that the output of ALL solar panels drops considerably during the shorter days and lower sunshine levels of Autumn<>Spring, and should not be regarded as a cure-all!