On 12/21/2024 at 5:24 PM, Iain24 said:

 

Thanks to Andy for the reassurance - I’m not worried so far, no problems. But we lack data on how extensive the problem is and what kind of use leads to battery failure.

Following a contribution above, apparently the only factor determining the level of charge is the time spent in ‘ready’ mode. The type of driving and environmental conditions are not relevant. That makes the calculations very easy. 

I have had the car 18 days and it has been driven just over 16 hours, with maybe another hour or so parked in ‘ready’ mode. In that time, the battery has gone from a charge of 12.8v to 12.2v. This means an average of about one hour per day in ‘ready’ mode is not enough to maintain the battery. It is, however, working normally at 12.2 although some have advised that is too low.

A trip of two hours plus twenty minutes in ‘ready’ two days ago did not shift the charge up from 12.2v. It was still reading 12.2 after the return trip which was broken into shorter segments. So four-five hours in ‘ready’ in a single day was not enough to increase the charge. I do wonder if the issue is about how effectively the battery gets charged rather than the battery itself.

In conclusion, I have not yet found what it takes in terms of normal use to increase the charge back to 12.8 or to maintain it at level. I will report here if I manage to work that out.

I hope this info helps someone, but if not please just tell me to shut up!

No problem with 12v battery For 3 Years... Mine Sits Anything between 11.8 and 12.2 ..Zilch Nadda Nil Problems.. !!!!!!!!!!!!!

2 hours ago, Thackeray said:

I wonder how low a 12v battery charge can go and the car still start without problems. I've seen my car start without any problems with the battery at 11.5v. So it was interesting to see the figures in the graphics below, with a car starting at 11.45v. This voltage only has to start the car's computer - I doubt it could start a conventional car with the need to turn its starter motor. 

But the state of charge figures don't make much sense. The first says 11.91% charge is 1% state of charge and the second says 11.45v is 0%. These percentages can't be accurate.

On 12/22/2024 at 5:16 PM, Heuer said:

Hit a new low:

Car still started though!

 

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On 12/23/2024 at 6:31 PM, Heuer said:

And today I went for the record:

Car started immediately.

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It's hard to find definitive information about AGM batteries as opinions seem to very a lot but the consistent two points I've come across are that you risk damaging the battery if you overcharge it; and secondly that AGM batteries tolerate deep discharge without damage. Maybe the car's charging algorithm aims to keep the charge below fully charged to extend the battery life. The hybrid battery is kept in a range of 40-80% and most often around 50-60%. Maybe the computer is doing something similar with the 12v battery in order to prolong its life.

I've seen charts of what percentage state of charge is represented by a given voltage on an AGM battery. (I think it was supplied by Herbie.) But I've now come across a different chart at this link. This page says that 11.9v would be 50%, which sounds perfectly adequate just to start the car's computer. Even the lower figure of 11.45v is put at around 25%, which the chart describes as "critical". But if it starts the car, the battery is immediately being recharged.

Has anyone managed to start the car at a lower voltage?

 

The pics shown above relate to the battery fitted to the LBX which is not an AGM battery but a FLA. Allowing the battery to fall below 50% SOC will damage it. I believe the battery shown in the pics above failed shortly afterwards and had to be replaced.

Correct, my battery did indeed fail after the SoC feel so low. I replaced it with a 45Ah which, so far, has not caused a problem.

To be clear the original Yuasa battery fitted to our LBX was this one, FLA, Made in Japan, dated 02/12/2023, 35Ah and CCA 240A:

New cars or in service replacement batteries seem to have a higher CCA of 264A but the capacity remains the same.

24 minutes ago, Emjay2 said:

The pics shown above relate to the battery fitted to the LBX which is not an AGM battery but a FLA.

Many thanks for clarifying that. I tried to find what kind of battery it was but had no success, so confess I took a chance and assumed it was AGM like on so many other of the hybrid Lexuses. That certainly means it will be damaged sooner by a low state of charge than may be the case for the other Lexuses that use AGM batteries. Locking you in the car when the battery fails doesn't seem like an attractive feature!

15 minutes ago, Thackeray said:

I took a chance and assumed it was AGM like on so many other of the hybrid Lexuses

All current models use flooded batteries.

58 minutes ago, Thackeray said:

Locking you in the car when the battery fails doesn't seem like an attractive feature!

Do you know that pulling the interior release buttons twice unlocks and opens the car so you would never be locked in?

3 hours ago, ColinBarber said:

All current models use flooded batteries.

The LBX's 12V battery is a classic FDL Yuasa 35 Ah 240 CCA. The CCA value on a hybrid car has no value, what matters are the Ah. The capacity of 240 Ah is ridiculously small. That said, to experience many happy Kms with the LBX you need to understand how the 12V battery is managed.

A retired electronics designer wrote a technically objective post on the subject.

The post is boring, but worth reading.

 

On 6/5/2025 at 11:05 AM, Thackeray said:

This voltage only has to start the car's computer

 Thackeray, this is not true. It supplies also other systems of the car, before READY.

Indeed. The 12V is there to energise the traction battery isolation relays which are mandatory on EV's and Hybrid's hence they all have them. 

On another failing battery note my key fob CR2032 battery gave up the ghost this morning leaving us locked out of the car. Fortunately the Lexus app opened the car and putting the fob next to the start button allowed it to start. No warning the fob battery was about to fail but fortunately I had a supply of them to hand. Second one I have had to change and they seem to last about 8 months so keep it in mind and keep one in the glove box!

1 hour ago, Lbeex said:

 Thackeray, this is not true. It supplies also other systems of the car, before READY.

It will supply ALL the car's needs before READY mode. Alarm, entry/exit system, welcome/puddle lights etc.etc.

On 6/7/2025 at 6:05 PM, Heuer said:

Fortunately the Lexus app opened the car

It didn't cross my mind. Smart.

Always use a replacement fob battery from a reputable manufacture.  I bought a couple of cheap batteries from an on-line supplier. Each of them only lasted a couple of months.

Mine were Panasonic Lithium CR2032 cells bought as a pack of six. They last about 6 months according to my wife who makes notes about these things!

2 hours ago, Heuer said:

They last about 6 months

What, in your LBX key fob!?

I haven't ever changed a battery in my Lexus fobs (approx 3yrs from new each time). Unless my dealership is doing it at service time...

Yes. Changed the factory supplied battery last October, changed the replacement last week. 

Quote

 Unless my dealership is doing it at service time...

You're having a chuckle 🤣

2 hours ago, NemesisUK said:

What, in your LBX key fob!?

I haven't ever changed a battery in my Lexus fobs (approx 3yrs from new each time). Unless my dealership is doing it at service time...

Same here on my IS 300h - in 8 years I've only changed it myself once when the car reported the key fob battery was low - as I have a service every 8 months I assume the dealer must be changing it. My car occasionally reports key fob battery is low, but I've found that is usually due to something in my pockets blocking the fob signal. 

2 hours ago, old man 2 said:

You're having a chuckle 🤣

Possibly but I think it is listed as part of the schedule..

The key fob issue relates to the LBX not the Lexus older models. The LBX uses the newest Toyota platform which does seem to be battery hungry both in terms of the 12V and the fob!

Hi, 

On 6/5/2025 at 1:45 PM, Heuer said:

Correct, my battery did indeed fail after the SoC feel so low. I replaced it with a 45Ah which, so far, has not caused a problem.

To be clear the original Yuasa battery fitted to our LBX was this one, FLA, Made in Japan, dated 02/12/2023, 35Ah and CCA 240A:

New cars or in service replacement batteries seem to have a higher CCA of 264A but the capacity remains the same.

Which battery model exactly did you install? Does switching to a non-original battery affect the car warranty? 

I bought my Lexus in July 24. In January 25 the battery was replaced with a new one at the dealership. A few days ago a low battery charge warning appeared at the Lexus app, so new original battery did not solve the issue for long.

The battery is a ‘consumable’ item, so replacement shouldn’t affect warranty. When I discussed this with the service manager at a Toyota dealership (Toyota hybrids have exactly the same battery issues) he said that so long as any future warranty repairs cannot be attributed directly to the battery then replacing it is not a problem. 

1 hour ago, Anmod said:

Which battery model exactly did you install? Does switching to a non-original battery affect the car warranty? 

I installed this one which costs about £65 delivered, case size LNO:

It is also referred to as the YBX5202:

 

No issue with warranty as the Drivers Manual states replace with "equivalent or higher":

And shows you how to access the battery: