LEXUS IS300h 12V battery problems/parasitic current

TheMcSame · June 8

On 6/6/2024 at 11:36 AM, Notamech said:

Sure thing. Il double check when i go to the car next but am pretty sure its this one https://www.yuasa.co.uk/ybx3053.html. Looks like its less than half the price and it fits and works perfectly.

Any quick rundown on what needs to be done while replacing it regarding any potential Battery management lark that might be in the car?

Never had the 'luxury' of changing a 12V on a newer car. Only older ones that didn't have any of this BMS lark to deal with.

Presumably it'll just be a case of get it all hooked up and reset it with a service tool (I.E an Autel or techstream)? Any issues just straight up disconnecting it (I.E Radio codes if that's still a thing) or is it going to be worth breaking out the OBD power cable?

Notamech · June 8

50 minutes ago, TheMcSame said:

Any quick rundown on what needs to be done while replacing it regarding any potential battery management lark that might be in the car?

Never had the 'luxury' of changing a 12V on a newer car. Only older ones that didn't have any of this BMS lark to deal with.

Presumably it'll just be a case of get it all hooked up and reset it with a service tool (I.E an Autel or techstream)? Any issues just straight up disconnecting it (I.E Radio codes if that's still a thing) or is it going to be worth breaking out the OBD power cable?

I didn't do it myself. It was done by the dealer who sold me the car. But from what i understand from others on this forum its a straightforward swap. Nothing needs to be coded. Some early models had an issue with the head unit failing after a Battery swap so would recommend switching it off before changing the Battery or better yet pull the fuse before changing.

TheMcSame · June 8

29 minutes ago, Notamech said:

I didn't do it myself. It was done by the dealer who sold me the car. But from what i understand from others on this forum its a straightforward swap. Nothing needs to be coded. Some early models had an issue with the head unit failing after a battery swap so would recommend switching it off before changing the battery or better yet pull the fuse before changing.

Really? I've heard others have had issues with the charging system killing batteries prematurely because the BMS wasn't sorted?

Unless it was something to do with the type of Battery it was and people wrongly assumed it was a BMS issue rather than the wrong sort of Battery?

Head unit is an interesting one though. But I'd imagine keeping power flowing to it via another means would keep things working fine.

IS300FSPORT · June 8

Can echo this having replaced the Battery on my driveway back in 2021. No need for any coding or reset procedure, there is no alternator to worry about overcharging the Battery the main traction Battery is intelligent enough to keep the Battery optimised.

Its as simple as ensuring ignition is off & remove the Battery clamp disconnect Negative first followed by positive.

Fit the new Battery & clamp it down ensuring vent tube is connected. Easy DIY just need a 10mm spanner from what I remember. Radio & Sat Nav continued working without any hiccup.

Maxz · June 9

22 hours ago, IS300FSPORT said:

Does your charger have a fuse to protect voltage overload & spark protection feature?

I have connected the Positive cable directly to the battery & negative directly to the battery countless times never had an issue. Connect the cables first then switch on your charger. Just be careful with the positive cable being close to the jack maybe cover it with a cloth.

For info I'm using the Noco Genius 5 I was connecting the crocodile clips directly to the battery. Now I have the quick connect lead permanently connected to the battery terminals literally plug and recharge once every couple of months don't need to remove the battery cover anymore either.

CTEK sell a quick connect lead

Here's my setup if it helps

Sorry extra question. I can see the Ctek cable comes with various eyelet sizes, m6, m8 and m10. Looking at how you connected and from measuring the diameter of the bolt shown, is m6 (6mm) the correct size?

Thanks again!

IS300FSPORT · June 9

26 minutes ago, Maxz said:

Sorry extra question. I can see the Ctek cable comes with various eyelet sizes, m6, m8 and m10. Looking at how you connected and from measuring the diameter of the bolt shown, is m6 (6mm) the correct size?

Thanks again!

Try M6 eyelet, M8 may have abit of play but once you tighten the nut down it will clamp on

I just checked my amazon order history the cable I ordered was M6 was a straight fit from what I remember.

Herbie · June 9

On 6/8/2024 at 12:14 PM, Maxz said:

This is what is concerning me about charging the battery from the boot per the charger instructions attached. Positive terminal can connect directly which is easy, but the negative not sure where to safely connect it.

The negative (-ve) Battery post is connected directly to the car body, which means that the whole of the body, ie, panels; screws; nuts; bolts; brackets, etc., at the front, back, top or bottom of the car - as long as they are clean unpainted metal (paint acts as an insulator so you don't want that) - can be considered to be the -ve Battery post and any of them will serve the purpose.

The only reason why they discourage connection directly to the actual Battery post itself is that the Battery could give off hydrogen gas and there could be a risk of explosion. Having said that, after more than 40 years of hobby-spannering, neither myself nor anyone I know has ever heard of an explosion actually happening.

The main thing to remember is - from an electrical point of view it matters not one iota where you connect the -ve lead to the car and I tell you this as a time-served, fully qualified electrician. When the factory closed down I became a telephone engineer on Post Office Telephones for the majority of my working life. Later on, after a back injury, I became a computer technician and hobby-wise I'm also a licenced radio ham.

I'm not trying to be obnoxious, big-headed, or blowing my own trumpet; rather just saying that I've been in the electrical and electronics fields for 50 years and I do have a bit of knowledge on the subject.

Maxz · June 11

The Battery has a wire joins straight to the chassis anyway as shown, so if you want to follow the "rules" to the T, you can connect negative here instead, or even connect on one of the 10mm socket jack bracket bolts (bolt thread is 6mm also). Given the positive terminal has the red plastic cover, risk of a short is minimal plus the Battery eyelet wires come with an inline fuse or you can add one (if your charger doesn't already have an internal one anyway).

Maxz · June 28

Thanks again all for the tips. Just to update have bought a new 12v AGM from Lexus, although the date stamped on the Battery is December 2023. 12.4v typically showing in Accessory mode and thus far not dropping away (if it does start doing this with the new Battery, then a new story begins...).

I looked at standard batteries and much of the feedback was you need an AGM for a start/stop vehicle due to the high frequency of charge and discharge cycles.

Also purchased the Ctek M6 terminal cable, which I plan to fit tomorrow. This will save me having to open the bonnet and remove the fuse box cover all the time which is a chore. The only logistics to work out will be where to run the charger or extension lead 240v cable out from, being sure not to create a possible water ingress point. I am hoping there is a point where the lower edge of the boot lid meets the bumper moulding, that has sufficient panel gap that a standard diameter power lead can fit between when it is latched.

Notamech · June 28

1 hour ago, Maxz said:

Thanks again all for the tips. Just to update have bought a new 12v AGM from Lexus, although the date stamped on the battery is December 2023. 12.4v typically showing in Accessory mode and thus far not dropping away (if it does start doing this with the new battery, then a new story begins...).

I looked at standard batteries and much of the feedback was you need an AGM for a start/stop vehicle due to the high frequency of charge and discharge cycles.

Also purchased the Ctek M6 terminal cable, which I plan to fit tomorrow. This will save me having to open the bonnet and remove the fuse box cover all the time which is a chore. The only logistics to work out will be where to run the charger or extension lead 240v cable out from, being sure not to create a possible water ingress point. I am hoping there is a point where the lower edge of the boot lid meets the bumper moulding, that has sufficient panel gap that a standard diameter power lead can fit between when it is latched.

While you are right you do need an AGM Battery for start stop vehicles yours is a hybrid not a conventional start stop vehicle. The 12V Battery is only used to boot or power up the computer. From that point on all Battery needs are handled by the traction Battery. Your engine starts are done by MotorGenerator1 in the gearbox which runs only on the traction Battery.

My advice to people looking to get a new 12v Battery would be to avoid the genuine Battery if your usage is not high. Theyre too small and fail too frequently if usage is low. But if your usage is high you should be fine with the original Battery they do last long if the car is used regularly.

wharfhouse · June 28

3 hours ago, Notamech said:

While you are right you do need an AGM battery for start stop vehicles yours is a hybrid not a conventional start stop vehicle. The 12V battery is only used to boot or power up the computer. From that point on all battery needs are handled by the traction battery. Your engine starts are done by MotorGenerator1 in the gearbox which runs only on the traction battery.

My advice to people looking to get a new 12v battery would be to avoid the genuine battery if your usage is not high. Theyre too small and fail too frequently if usage is low. But if your usage is high you should be fine with the original battery they do last long if the car is used regularly.

My 12V Battery in my 2014 IS 300h that has now done 149k miles is still the original one. I have just left the car for 10 days while I was away and it started no problem when I got back. The Lexus OEM batteries are in my experience (based on other cars and batteries) very good but the car needs to be used regularly and long enough for the 12V Battery to properly recharge (mine is - hence the mileage) but this is the same with all modern cars with their electronics and alarms etc. - gone are the days of leaving a car months and expecting it to start on returning. If the car is being left weeks with no use or only short runs between the some sort of Battery charging is a must.

Maxz · June 29

21 hours ago, Notamech said:

While you are right you do need an AGM battery for start stop vehicles yours is a hybrid not a conventional start stop vehicle. The 12V battery is only used to boot or power up the computer. From that point on all battery needs are handled by the traction battery. Your engine starts are done by MotorGenerator1 in the gearbox which runs only on the traction battery.

My advice to people looking to get a new 12v battery would be to avoid the genuine battery if your usage is not high. Theyre too small and fail too frequently if usage is low. But if your usage is high you should be fine with the original battery they do last long if the car is used regularly.

You do have a valid point there, that the vehicle is hybrid and not a standard start-stop vehicle. What I also found is all other Battery retailers, when you input your vehicle or registration to search, they all stated "go to dealer". If this one again dies within 2 years will defo go for a non-AGM.

Below got the "quick" trickle charge setup in place. For anyone else interested there is a convenient access point that you can stow the connector end in. This way you dont have to take off the main trim door each time. Given the base of it is metal I also opted to line it with some plastic to avoid any risk of shorts although highly unlikely.

Note that to get the red plastic positive terminal cover to clip back into place, you can cut two small channels to create a bendable tab that allows the eyelet cable to poke out.

Given I went for a standard instead of indicator Ctek cable which does not come with an inline fuse as standard, opted to add my own per photo. I happened to have a glass fuse holder to hand so used that, but otherwise a car-fuse type holder is best (looks nicer).

TheMcSame · June 30

On 6/28/2024 at 5:00 PM, wharfhouse said:

My 12V battery in my 2014 IS 300h that has now done 149k miles is still the original one. I have just left the car for 10 days while I was away and it started no problem when I got back. The Lexus OEM batteries are in my experience (based on other cars and batteries) very good but the car needs to be used regularly and long enough for the 12V battery to properly recharge (mine is - hence the mileage) but this is the same with all modern cars with their electronics and alarms etc. - gone are the days of leaving a car months and expecting it to start on returning. If the car is being left weeks with no use or only short runs between the some sort of battery charging is a must.

Damn... Reminds me of the old Fiesta... 15 years the OEM Battery lasted.

That being said, I think it's largely luck of the draw. My IS is 4 years old, 56k miles (54K when I got it), so its averaged maybe about 1K miles less a year? After a solid week of driving (Up to Highlands to do the NC500 and back), it seemed like the best it could muster was about 11.7V IIRC.

Malc1 · June 30

Modern batteries coping with modern cars and their copious electronics and parasitic drain issues …….. just aren’t up to the job …….. and seem to ( often ) fail while under the guarantee period …… or within too short a period anyway

vide:

My 2006 Honda Legend ….. £160+ Varta Battery failed 4 years into the 5 year warranty …… the replacement lasted just over a year ……. give up on Varta …… this new replacement wouldn’t hold any charge after failure 🤔

Nephew tells me his 12v Battery will cost him £600 to replace in his 2013 Range Rover …… whichever model it is

My 1932 Triumph Southern Cross Sports Tourer simple 12v Battery is £66 👍….. zero electronics helps

My 91 Ls400 Yuasa 5 yr gtee Battery was @£165 last year ….. little electronics to cope with …… seems and “ feels “ brilliant every day …… so far !

I just don’t think they make car batteries sufficiently robust, whatever the cost, to cope with the electronic drain modern, newer cars put upon them

Battery manufacturers really need to “ up their game “ ……. simply not fit for purpose 🥵

Malc

Herbie · June 30

2 hours ago, Malc1 said:

Battery manufacturers really need to “ up their game “ ……. simply not fit for purpose

Not sure I agree with that Malc.

Remember that Lexus/Toyota don't manufacture batteries, they just buy them in from people who do manufacture them. This means that they are consciously making a decision to buy low electrical capacity batteries. Higher capacities of, say, 75Ah, 100Ah and even 120Ah are being manufactured and are readily available but Lex/Toy just choose not to use them.

Malc1 · June 30

Hi. I’ve never bought a brand new Lexus so don’t know the OEM level of Battery quality robustness ……. all my Battery replacements that I’ve personally bought over the years have been of max Ah irrespective of cost …… I just don’t want the inconvenience of a failure ….. always at the worst possible moment I’ve no doubt

BUT for Lexus to effectively, on a brand new car, skimp on the Battery quality is just terrible and unforgivable……..

Doubtless all other common manufacturers operate this same skimping principle ……. to save pennies and destroy their reputation …….
An £80/100k Lexus car with a crap Battery at new is disgraceful …… well, as is any brand new showroom car ……

Not sure I’m ever going to buy a brand new car again whatever ( hahaha my first and last a Hillman Imp in 1969 at age 19 )

2ndhand older Lexus Ls400s have been brilliant for me ….. for a decade or several now 😂

I really pity all these Lexus owners suffering this OEM breakdown in relative competency and understanding of their Client needs

Malc

Notamech · June 30

49 minutes ago, Malc1 said:

Hi. I’ve never bought a brand new Lexus so don’t know the OEM level of battery quality robustness ……. all my battery replacements that I’ve personally bought over the years have been of max Ah irrespective of cost …… I just don’t want the inconvenience of a failure ….. always at the worst possible moment I’ve no doubt

BUT for Lexus to effectively, on a brand new car, skimp on the battery quality is just terrible and unforgivable……..

Doubtless all other common manufacturers operate this same skimping principle ……. to save pennies and destroy their reputation …….
An £80/100k Lexus car with a crap battery at new is disgraceful …… well, as is any brand new showroom car ……

Not sure I’m ever going to buy a brand new car again whatever ( hahaha my first and last a Hillman Imp in 1969 at age 19 )

2ndhand older Lexus Ls400s have been brilliant for me ….. for a decade or several now 😂

I really pity all these Lexus owners suffering this OEM breakdown in relative competency and understanding of their Client needs

Malc

I agree. The forum is rife with peoples batteries dying too often that too on brand new cars like the LBX, NX, Yaris etc. I feel like Toyota has had enough time and experience to learn that these batteries die within just a few weeks of no use. I feel like they should have updated the batteries accordingly. Also im not very familiar with Battery chemistry but it seems like these newer AGM batteries are to be thrown away when they fail. I remember when lead acid batteries would last virtually forever with people using old school high voltage chargers to just boil off the sulphation. Add distilled water and its good as new.

Maxz · July 3

Also if someone can tell me if my maths is correct or incorrect here.

Checked voltage in accessory mode this morning @12.2V.

Based on the AGM chart on this website (Ultimate Guide to Battery Voltage Chart (ecoflow.com)) that is about 65% charged.

The capacity of a 28800-YZZA1 Toyota AGM Battery is 45Ah.

My Ctek XS800 maintenance charger delivers a maximum current of 0.8A.

Based on this and using this website (Battery Charge Time Calculator - Footprint Hero) I get 25 hours to recharge the rest of the way to 100%.

Sound right or have I got something wrong here? I recharged the other day for 4-5 hours from 12.2v and the Battery was showing 12.9V (almost 100%) immediately afterwards but I have read this voltage is overstated due to residual charge and needs to be left resting for a period of time so that the resting/true voltage reading is given.

Leaving on charge for 25 hours, just a bit nervous of overcharging but assume 0.8A is not a strong current anyway and if working correctly the charger should switch automatically into maintenance mode anyway, dropping to an even more nominal current.

Many Thanks

IS300FSPORT · July 3

I have experimented with Battery voltage before now & too many different readings.

After a full charge within 24 hours it gradually seems to rest around the 12.3.

You need to remember as soon as you open the Drivers door your consuming voltage from the 12v Battery, it charges the brake module before even pressing start, & even more voltage when your in accessory mode as its powering up all the computers. If on auto Headlights, wipers, etc

Another way is to measure it in the morning (resting voltage) is what your looking for to get a real indication of the charge its holding. Use a volt meter from the boot connecting directly to the Battery that way your not waking up any of the computers.

Although I now have a permanent hardwired Bluetooth module connected to the Battery 'Victron energy smart Battery sense' I can monitor the 12v without waking up the car sat in my front room. Typically after a drive it seems to rest around 12.5-12.6v. Charging it once a month never ran into any issues even if its stood for a week 12.1v is the lowest iv seen it with a dash cam activated in parking mode when I'm in suspect areas.