Booster Battery to jump start 2018 RX450h

dgw1 · July 12, 2022

I see that this topic has been discussed quite a lot but sorry, I still have some questions : My new, four year old 450H, with only 3800 miles, has now had a RoadAngel Pure hard wired into it. The technician that did it had a lot of trouble finding the right wire to join into and stopped and started the car about 20 times over about 1 ½ hours. That drained the Battery. No surprise there. I learned how to jump start the car from the engine bay because he had to find out how to do it. He used his huge booster jump start Battery. Two days later the Battery has insufficient power to start up again so I put it on trickle charge using my mains charger with the +ve post in the fuse box in the engine bay and -ve to a chassis nut and checked the following morning and the Battery reads 12.59V on my digital meter which I understand is correct for a fully charged Battery. Also the cells are nicely covered with liquid and don't need topping up with distilled water. So hopefully that is that.

Two questions : For precaution, I am thinking of keeping in the car the Clarke Jumpstart Micro 400 which is one of the new Lithium Battery very small booster batteries - in case I get caught out again when not at home where I have my mains charger and engine starter. This Clarke is Starting 400A / Peak 800A. And it has really quite thin short cables - hugely thinner than the massive cables on the Technician's big Booster Pack. So, will this Clarke model jump start the car if the Battery goes flat again ?

My second question : The -ve post next to the red +ve post in the fuse box. It seems this should not be used for the -ve cable being used to jump start or charge the Battery. Why not ? The clamps and cables on the Clarke would easily fit on both posts. is this permissible ? Is it only a precaution to use a chassis post or nut for the -ve cable, or mandatory ?

Third Question : The small 12V Battery in the boot. I do understand that this does not start the engine and it sets the relays and the computers and some ancillary equipment such as radio and lights. But is it a good idea to try and get a larger capacity Battery ( if it will fit in the space ) to stop it becoming drained quite so easily ? Has anyone done this ? it seems that most batteries are too high to fit inside the space.

Any help most appreciated !

Herbie · July 12, 2022

First of all, this chart is quite useful:

I don't know much about the Clarke jump starter but as Machine Mart seem to be the only place selling Clarke stuff, I'd stay away from it just on principle. I've always found Machine Mart to be way overpriced. I got the Tacklife T8, which was about £60 at the time but I believe it's been superceded by an updated model now, something like the one below:

These things look small and do indeed have thin leads, but they do pack a punch and will start most cars without even breaking a sweat. This is especially true of hybrids because the system only takes around 20A to achieve READY status. I went for a fairly beefy one so that I could offer a jump start to someone with a conventional car if they needed one, because although it's perfectly safe for a hybrid to receive a jump from a conventional car, you should never use a hybrid to jump a conventional car.

Regarding the -ve post in the fusebox that you mention - I'm not sure there is a -ve post in there. If you mean the bare nut that I've connected to in the photo below, that's another +ve one, not a -ve one:

If your fuse box is different and it is actually a negative terminal then yes, it would be safe to use it.

The advice to use an unpainted nut/screw/bolt as the negative refers to the Battery posts. A charging Battery can cause gassing and if there are any sparks generated by removal of the negative lead, it could cause an explosion. From an electrical perspective, it makes absolutely no difference whatsoever whether the negative lead is connected directly to the -ve Battery post or to some other part of the car.

Your final question opens a can of worms. Fitting a larger Battery can be done but may require some modification. Electrically, a larger Battery will hold charge longer, but is it worth all the faffing around? Only you can answer that one.

Barry14UK · July 13, 2022

If you have a small 12v Battery beneath the tailgate and it is the original or is an original replacement, it is likely to be a Panasonic VRLA AGM rated at 51Ah like Herbie and I had on our 3rd generations.. This is a very small but expensive Battery. It has been suggested that Lexus fitted the AGM type because the electrolyte is held within the mat which means that in the event of an accident there is reduced risk of acid affecting passengers than would be the case with a free flowing lead acid version. However, if you accept this small risk as some have, you can fit a free flowing other make acid Battery of the same size as the Panasonic which is not only cheaper but gives 60Ah from memory. The limitation of size is because of the small compartment size Lexus allowed for the Battery.

I did modify the plastic tray and do a few other mods to enable an alternative AGM Battery to be fitted which I did post on this forum with pictures. This also gave 60Ah but was considerably less expensive than the standard Panasonic and was of a size more readily available than the Panasonic. As Herbie says, was a bit of a faff but I wanted to prove a point and still have an AGM Battery.

Batteries should not be allowed to go flat, particularly AGM ones as it seriously reduces life. AGM 12v batteries need to be charged with a smart charger using AGM mode and limiting charging to 5A.(this reduces as Battery becomes near fully charged). Other ways to charge the 12v Battery are to use the car, including statically as Lexus set out in the owners manual or via fitted small solar panel.

As Herbie said, only a small power source is required to power up computers etc to powerup your Lexus.

You might find this video on testing jump starters interesting, (one of many tests done by Project Farm on products).

Illogan · July 13, 2022

18 hours ago, dgw1 said:

I see that this topic has been discussed quite a lot but sorry, I still have some questions : >>>>>>>

Any help most appreciated !

David, I've been through similar experiences to you, and you'll find that Herbie and Barry's comments are comprehensive, and contain all the information you need.

(and I keep a Genius Battery Booster in my car)

dgw1 · July 13, 2022

Thanks all for excellent info. The 12V Battery, since being drained by the RoadAngel installation, keeps on losing its charge. I have to jumpstart it via the engine bay posts. It starts immediately and then the Battery readout is 13.5V. It is not any AGM. It is a 460A 60Ah wet cell with removable cell covers.

1. I assume this means the Battery needs replacing and is not indicative of some other fault ?

2. When he car was stopped and started 20 times in 1 ½ hours, during the road angel installation, did that kill the Battery or would that not kill a healthy Battery. If they killed the Battery, they are responsible for a new one.

3. I can change the Battery myself but need to understand how to do it without disconnecting power so that I don't have any reset issues. I had big reset issues when the Battery in my previous 2010 RX450h was removed. Lexus Tonbridge Wells insisted I needed a new £1000 boot lid motor. I insisted it just needed a reset. The argument went on and on. They were absolutely sure and ordered the boot lid motor from Japan. The day I was going to take the car to them to have the job done, it reset itself ..... So I don't want any reset issues when I change the Battery which looks like what I will need to do.

Hopefully when this is all answered, it will be the end of this topic !

Huge thanks to Herbs and Barry and everybody else.

Herbie · July 13, 2022

1. Possibly, but not necessarily. Once you've jump started it, are you taking it for a good run (at least an hour, preferably two or more) or are you just doing short journeys and not giving it time to charge?

2. The system works this way: Let's say that you're sat in a car park waiting for someone and you want to listen to the radio. If the car is in ACC mode then you may get about 20-25 minutes of the radio before a message comes up onscreen saying that the radio has been turned off to avoid a flat Battery. However if the car is in READY mode, instead of shutting the radio down, the hybrid system will fire up the engine to keep the Battery charged up, and it will do this cycle as often as needed.

So, when they fitted the Road Angel, was the car in READY so that the engine could fire up as and when necessary? If so, then it wouldn't have flattened the Battery unless something was wrong with it anyway. If the engine was firing up then it was actually helping the Battery, not killing it.

3. All you need to do is to connect another 12V source to the cables immediately before you release them from the Battery posts. The little jump start Battery pack would be ideal, but you could even do it with a pack of 8 AA batteries.

EDIT: I have no idea what a 'Road Angel' is but are you sure it's not that that's draining the Battery?

Haylands · July 15, 2022

When measuring the voltage in a Battery after charging you should wait at least 30 mins after disconnecting the charger before using a meter to check the voltage, the Battery needs to settle to give an accurate reading....

Haylands · July 15, 2022

On 7/13/2022 at 7:41 PM, Herbie said:

EDIT: I have no idea what a 'Road Angel' is but are you sure it's not that that's draining the battery?

Herb,

It's a device people who exceed the speed limit use to warn them of cameras...

Herbie · July 15, 2022

38 minutes ago, Haylands said:

When measuring the voltage in a battery after charging you should wait at least 30 mins after disconnecting the charger before using a meter to check the voltage, the battery needs to settle to give an accurate reading....

And just to add to that - for even greater accuracy, a multimeter isn't really any good. It needs a proper Battery tester that simulates a load. A multimeter may show, say, 12.6V but once a load is applied, that may drop like a stone if there's a bad cell or something else wrong.

Haylands · July 16, 2022

Just had a thought, doesn't the RX450h engine get started by the motor generator? in which case it's the big Battery that starts the engine, not the 12v one...???

Herbie · July 16, 2022

1 hour ago, Haylands said:

Just had a thought, doesn't the RX450h engine get started by the motor generator? in which case it's the big battery that starts the engine, not the 12v one...???

Yes Peter, that's correct.

The 12V boots the computers and operates a 12V twin-relay interlock to bring the hybrid system onstream and into READY mode. After that, the hybrid system charges the 12V Battery via a DC/DC converter that converts the 288V from the traction Battery to about 14.5V to run the 12V systems and also charge the 12V Battery.

The most worrying thing about this is that, to quote the OP:

Quote

The technician that did it had a lot of trouble finding the right wire to join into and stopped and started the car about 20 times over about 1 ½ hours.

All he needed was to read the fuse box label and find one that is ignition-switched. Even if the fuse box lid is missing, two minutes with a multimeter would have found one. I'm beginning to wonder if he's wired it to a permanent 12V supply and this is the cause.

EDIT: Another very worrying point:

Quote

I learned how to jump start the car from the engine bay because he had to find out how to do it.

What sort of technician doesn't know how to jump start?

This job wasn't done at Halfords was it David?

Haylands · July 16, 2022

So the OP doesn't need a jump start pack, any 12v supply would be enough to get the car switched on, whereby it will charge the 12v Battery up itself...?

Herbie · July 16, 2022

2 minutes ago, Haylands said:

So the OP doesn't need a jump start pack, any 12v supply would be enough to get the car switched on, whereby it will charge the 12v battery up itself...?

Yep. In theory at least, although a small jump start Battery pack is really the way to go and it's very handy to keep in the car.

dgw1 · July 16, 2022

No, definitely not done at Halfords. Done by RS Telemetrics who are one of the National Companies that RoadAngel use for their installations. It was a brand new Battery he killed. A Panasonic full flooded with removable cell caps for topping up - NOT AGM - that Lexus put in one week before I bought the car. As concerns jump starting it, he had to find out that you must do it via the =ve Post in the relay and fuse box in the engine bay. I can understand that, if you have never done such a Lexus Hybrid car before. The car is a 2018 RX450h Premier and only done 3800 miles. This morning I bought a Toyota drop in replacement Battery - the correct size from my local Toyota main dealer. And with the necessary vent pipe outlet. And 540A instead of the Panasonic 460A. £96 versus £230 for the Panasonic one from Lexus. Might be interesting for other users to know that Toyota make a direct drop in replacement! And it is sealed, not open cells like the Panasonic! Fitted it myself with the misses helping and used the micro lithium pack to not lose power during the changeover as Herbie recommended. Problem over ! Thanks everybody - such a good forum.

Illogan · July 16, 2022

Great stuff David, delighted your problem's been resolved, and good to learn that Toyota do an alternative Battery.

Thanks for the update.

Herbie · July 16, 2022

55 minutes ago, dgw1 said:

Done by RS Telemetrics who are one of the National Companies that RoadAngel use for their installations

Hmm, good to know - one in the list of companies to never use.

57 minutes ago, dgw1 said:

As concerns jump starting it, he had to find out that you must do it via the =ve Post in the relay and fuse box in the engine bay.

I don't know who told him that but it's utter codswallop. It's perfectly acceptable to do it that way and probably more convenient too, but it's equally as acceptable to connect jump leads to the Battery itself, under the floor of the boot.

1 hour ago, dgw1 said:

This morning I bought a Toyota drop in replacement battery - the correct size from my local Toyota main dealer. And with the necessary vent pipe outlet. And 540A instead of the Panasonic 460A. £96 versus £230 for the Panasonic one from Lexus.

I would imagine that that's the CCA (Cold Cranking Amps) rating. It's good to know, but in reality it doesn't make a difference to the hybrids (a) because it doesn't crank the engine, and (b) it only takes around 20A to get the hybrid system up and running in READY mode.

Fingers crossed that it's all sorted for you now mate, and that you can just get down to the business of enjoying the car :thumbup:

Barry14UK · July 16, 2022

Interested to learn that Lexus fit a non AGM with screw tops to cells Battery for 4th Generation, unless the particular Lexus dealership you bought car from put in a cheaper non original spec one for expediency. If/when you trickle charge it, the correct mode on the smart charger should be used for AGM or normal, depending on type of Battery fitted.

ColinBarber · July 17, 2022

8 hours ago, Barry14UK said:

Interested to learn that Lexus fit a non AGM with screw tops to cells battery for 4th Generation, unless the particular Lexus dealership you bought car from put in a cheaper non original spec one for expediency.

Lexus seem to be using standard flooded batteries on all their new vehicles, we’ll certainly on the UX, ES and RX anyway.

Barry14UK · July 17, 2022

3 hours ago, ColinBarber said:

Lexus seem to be using standard flooded batteries on all their new vehicles, we’ll certainly on the UX, ES and RX anyway.

Yes Colin,

I have just checked prices with Lexus Parts Direct who state that they only supply genuine replacement parts. I don't know what 12v Battery the 4th generation came with but they now give the ref for this as SKU: 28800-YZZZA RXP4 with a price of £71-49, retail. (You will not get an AGM Battery for this sort of price so it must be a standard full flow model)

For the 3rd generation they have dropped their price to £140-02, the reference to it being SKU; 28800-31291 RXP3, so this could still be an AGM model as originally fitted albeit at a much lower price. Maybe Lexus will use up stocks of this Battery and then change to a non AGM one as fitted in the 4th generation. This is just speculation on my part but would appear to be logical progression. If this is indeed the case it begs the question as to why anybody with a 3rd generation and some further models further back, should not opt for an appropriate non AGM model if they need one now.

Illogan · July 17, 2022

2 hours ago, Barry14UK said:

Yes Colin,

I have just checked prices with Lexus Parts Direct who state that they only supply genuine replacement parts. < > , should not opt for an appropriate non AGM model if they need one now.

That is an excellent observation Barry

ColinBarber · July 18, 2022

On 7/17/2022 at 12:31 PM, Barry14UK said:

it begs the question as to why anybody with a 3rd generation and some further models further back, should not opt for an appropriate non AGM model if they need one now.

I don't know how sophisticated the charging circuitry is but AGM batteries typically need a slightly higher charging voltage so you could impact a flooded Battery if the vehicle wasn't designed for it. Possibly the circuitry wasn't optimised for AGM in the first place and you would be ok but you would want to keep an eye on the electrolyte level.