I have to agree with WellsB's comments. I think that it is a CYA statement. I prefer a dedicated harness on my batteries to charge them, while mounted to the vehicle, I have also used clamp-on type connectors at times, in the past. I have several .75A float chargers as well as a 1A and 5A charger from NOCO, which also go into float mode after charging is complete. I've had no issues ever with any of them and I always keep a float charger on my motorcycle and one on my Vespa in my garage. I have rarely charged a battery out of the vehicle.

 

I purchased this battery tester, here are more expensive units. I am quite pleased with it to give me an idea of the battery capacity when fully or partially charged. It also measures CCA cold cranking amps of the battery.
I used this on my vehicles . I will tell you however, that for the my hybrid 12v battery, I found that the capacity of CCA of the battery measures more than that of the factory specifications. On my non hybrid cars, it reads CCA inline with what the car battery indicates on the battery.
I have NOT disconnected my 12v battery post cables to measure CCA .

MOTOPOWER MP0515A

The best place to measure is at the battery posts, not up front in the engine compartment...at least not for my hybrid.

 

Tested my RX450h+ OEM battery, 6 months after testing it new to establish a baseline. It shows only slight degradation. Keep in mind that I fully charge it about once a month.

Readings are baseline then 6 months later;
540 / 521 CCA (345 claimed CCA)
189 / 183 MHO internal conductance
5.27 / 5.46 m ohms internal resistance

The MHO reading is the main one I'm looking at. 70% of baseline is considered end of life. I'm at 97% of baseline at 6 months.

 

Just to be clear, I'm using the term fullly depleted in reference to state of charge of the battery, not end of life. Having to jump start means the battery is fully depleted or too low of a state of charge to start the vehicle. It does not mean the battery is at end of life, though repeated deep discharges of a starting battery does shorten its lifespan. There is an element of chance in whether a battery can recover from a deep discharge, and how long the battery stays in a deep discharge condition has an effect as well.

 

Thanks for all the guidance. I finished the charging mostly at 5 Amps (started at 2 Amps initially to check for any excessive heat from the charger, and switched to 5 Amps after about 2 hours). It took about 8-9 hours to reach full charge. So I reckon that's about 40 Ah in the stock 60 Ah battery - which was still functioning before this external charging (i.e. did not need jump starting and ran for about 1 week with 100+ miles, after the 2 jump starts during the cold spell). That shows Lexus' 12 V charging subsystem in very poor light - just as you might expect from LSFT's long-term measurements. Stefanos - if you do similar measurements on the RX450H+, please let us know.

The charger I got has the built-in test for the battery at the beginning and end of charging. The end of charging part I was particularly interested in, to confirm if the battery can actually hold charge after the torture from Lexus' charging subsystem. It seems to have passed, as the charger reached the final "FUL" state of 100 % charge. In my 6 month/5K service, I will still ask the dealer to replace the battery under warranty, since it has already needed 2 jump starts (and we all know how bad the 12 V charging system, all on Lexus. At least I'm doing Lexus a favor and not trying to trigger Lemon Law).

Now the next question is: Given all that we know, how frequently do I have to nanny the 12 V battery with the external charger - is about once a month sufficient ?

 

My Lexus dealer service dept told me that a vigorous documented printed out test has to be submitted with battery warranty that they have to follow and cannot just replace the battery. If they charge it and it passes tests they will not replace.

 

An update on the 12v battery parasitic draw for the new 2024 RX 450h+, where the vehicle 12v battery was 'dead' twice first week of ownership.

The local Lexus dealer has had the vehicle for ten days now, diagnosing and running tests. I'm told a (regional ?) Lexus engineer has visited the dealership during the process, providing guidance, probably asking questions. I don't have any real concrete answers, "aha" moments, or practical info on tests run, solutions found. What I am told - Thurs last week - is that they have observed the 12v battery (sitting in one of their garage bays this whole time) drop daily down to 11.8v. I'm being told this could be 'normal'. Doubt that, as my understanding is 11.8v on most 12v car batteries is a rather deep discharge.

I don't believe a brand-new $70k+ Lexus should have to have a trickle charger added daily to prevent a 'dead battery' situation with the vehicle, so yes: if this isn't resolved, we'll pursue the Lemon Law process.

 

In there tests can they tell amount of parasitic draw over a time period like 24 hrs? That would be smoothing out the ups and down of the draw and give an accurate total and that is what needs to be looked at to see if it is excessive. There entire lineup is facing similar problems just seems to be more severe in some like yours. For yours to be depleted within 1 week is not normal. If they think that is normal then a salesman when demonstrating a car on the lot would have to charge the battery just to test drive. As for the lemon law especially here in NC it is almost impossible to do but in other states I have heard all you have to do is hand the keys back over with no repercussion.

 

Any lemon law buyback is done by Lexus and not the dealership. Lexus will tell you when and how to return the car they are buying back.

 

So it's been sitting there for 10 days. It would be interesting to see whether they can restart it after 14 days...2 weeks. if so, then that seems like a typical modern car to me? Many sites suggest anything more than 14 days standing is iffy for 12V batteries, and that has always been my understanding too.

 

It depends. VW and Audis go into a deep sleep with the car after 7 days to avoid this. Ford does it as well I believe.

 

Mine 450h+ has been sitting in the dealership for 12 days. New battery did not do the trick. Today they declared they found the source of battery drain. It is a DCM that is bad. They replaced it. I have not gotten the car back yet but you may want to share this with your dealer. Since we are not the only unfortunate ones who had this kind of issue. My car is 1 month old. I am ready to turn it back to Lexus.

 

...And therefore they didn't bother dealing with the vigorous document and sent you home?

 

It is defective in what way? Communication to network too much? Or something else? Thanks.

 

I disagree, my previous 2021 X5 45E PHEV sat in the garage for weeks and sometimes over a month without being driven and never once I had to jump it. It had the same app and digital/proximity sensors/features as the RX450h+ (maybe even more, I love that I can unlock and drive that car just using my Apple Watch).

This is just **** poor battery management system that Lexus has.