Hook up a battery tender on my 2021 ES350?

[Natty Bumppo]

I will be leaving the car parked in my garage for several weeks and want to keep the battery from dying. On these high tech electric cars that need battery power 24/7 can I just simply connect the battery tender to + then  - posts, and plug tender into a wall outlet? Or is this not recommended for these high tech cars?

My battery tender has 1.3 amp supply.

Thanks all

 

 

[Dean2]

Post I wrote earlier. Hope it helps.

 

Pictures at this link.

 

https://www.clublexus.com/forums/ls-4th-gen-2007-2017/1025956-ls460-batteries-parasitic-drain-battery-life.html

In addition to high temperatures killing batteries prematurely, leaving cars sit and letting the battery drain down then recharge, dramatically shortens battery life, no matter what kind it is.

In order to understand how quick this happens on our heavily computerised cars I thought, I would run the test on my 2015 LS460 SWB AWD. I started with a quality Multimeter that has both DC and AC current(AMP) measuring capacity. You put the black lead into the common port, and the Red lead into the 10A port, may also be labelled just AC/DC A on some meter. Having Alligator clips on the end of the probes will make doing this a whole bunch easier.

I shut off the car, put the key FOB in the house in an RFID box, left the doors unlocked, and lifted the hood. My car does not have a hood open warning light so no hood open sensor that needs to be defeated. I disconnected the negative terminal on the battery, clipped the Red Lead to the battery terminal and the black lead to the Negative cable. I then opened and closed the drivers door. Reading popped to 4.8 amps with the interior lights coming on. Closed the drivers door, reading dropped to 2.7 amps and after about 30 seconds started to steadily drop. Within 90 seconds it was down to .7 amp and still dropping. Within three minutes it was reading between .03 and .04 amps, so 30 to 40 Miliamps.

I had read that the FOB being too close would cause the vehicle to wake up so I went in the house and got the FOB. Even right beside the car, not change in .03-.04 AMPs being drawn. Used the FOB to open the trunk, reading popped up to 6 Amps. Closed the Truck with the auto close system using the button on the trunk lid, reading stayed at 5-6 AMPs. As soon as the trunk latched the AMPs dropped to 2.5 and then kept dropping following the same pattern above. I tried a number of different combinations and permutations, including putting the push button start in the run position without stepping on the brake so the car didn't start. Remember, your multimeter is limited to 10 AMPs, if you start the car, or turn on high draw things like Headlights, you will likely pop the fuse that protects the multimeter.

No matter what combinations I tried, the at rest reading dropped back to the 30 to 40 miliamp reading. The only thing I didn't do that I wish I had done, was lock the doors and see if the at rest reading increased with the security system active. Since I park in a secure garage and never lock the car, I didn't think about that till I had it all buttoned up again.

Since the car sits for long periods of time I have attached a NOCO harness to to the battery terminals to make hooking up the trickle charger much easier. This way I can just plug the trickle charger in without having to remove the clips and lift the battery cover each time to attach alligator clips. I have these quick connects on all my vehicles. Even at only 40 Miliamp, a battery will drop below starting voltage in about a month, if it is stored cold it will go flat faster than that. Remember, lead acid batteries do not like to be discharge down to 11 Volts and recharged. They are much happier and last far longer if kept above 12.3 volts and that means a trickle charger is a good idea if you don't drive your car for at least 30 minutes every 3 or 4 days.

Hope this information helps those of you suffering from batteries going flat or dying prematurely.


















Multimeters have a lot of different layouts, this is just for illustration.













As a followup, Charged the battery to full, after an hour off the charger, read 12.73. July 2023 OEM Lexus battery. After sitting in the garage un-driven for 8 days, battery now reads 12.45. So the constant drain, even though very small, definitely draws down the battery over time. Battery went from 100% to 80% in 8 days. Still lots of juice to start the car. Left parked with no trickle charger, and assuming an even rate of drain the battery will be down to 50% in another 12 or so days.

At 12 Volts it is still enough to start the car but this is NOT what lead acid batteries like and will materially decrease its service life. If you aren't driving the car regularly your battery will last far longer if you put it on a .75 AMP to 2 AMP smart trickle charger like a Noco. The other option is to disconnect the negative battery during storage, but I find it a lot easier just to leave it on the trickle charger.


You can use the quick connect cable on the jump start terminals as well, they don't have to go on the battery itself. The reason I put them on mine was so I don't have to remove any of the under hood covers or the battery cover to hook up alligator clips each time I wanted to put the trickle charger on. On my LS you can't reach the battery terminals without opening the battery cover by the windshield.

Here is a picture of the LS460 Battery location. The panel with the Yellow sticker has to be removed at min to get alligator clips onto the battery.

 

[Natty Bumppo]

Thank you Dean2

Great information, lots to read. So I without issue I can connect the tender to the battery while the battery is in the car with the + and - cables connected. I would close the hood when the tender is on since my car has  a hood open sensor that shows a hood open red light on the dash cluster. 

Q- When you were doing the volt - amp testing with the - cable disconnected and 12v  gone from ECU what did you do to restore the computer settings after reconnecting the ground?  

I have done that amp draw testing on cars that are not so high tech but I am hesitant to do that amp draw testing on this car since the 12v will be gone and I am concerned about how to return all the settings.  

Have a good day

Peter

 

 

 

 

 

[Dean2]

With mine I never lost any settings. Most cars dont lose anything that the owner can't easilt reset but if you are worried about it use a 12 volt supply that plugs into the cigarette lighter or USB Port to keep power to the ECU when you disconnect the battery.

Use a smart trickle chrger like a NOCO. Mine goes into standby when the battery is fully charged, kicks back on when needed, then cuts off again. You can leave a NOCO 750 milliamp to 2 amp hooked up full time to take care of the battery. My Nocos even have seperate settings for flooded lead, AGM and lithium batteries.