Dean2

Post I wrote earlier. Hope it helps.

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.

Dean2

A bit of an update to my post above. Have had the LS460 on a battery tender all winter. Car hasn't been driven for about 35 days, prior to unplugging the tender. Took it off two weeks ago as I was going away and didn't want to plugged in while I was gone. Got back, measured the battery voltage, still at 12.67 after 14 days just sitting.

So the good news is, for longer term sits the car must go into a deeper sleep than what I was first measuring. Once it has sat un-driven for a month or so, the draw must drop to nearly nothing as 12.67 is virtually a fully charged battery. If the draw had remained at even 40 Milliamps, it would have drawn it down more than that.

So a battery in good condition, and a car stored in heated indoor storage, no alarm armed, appears to be able to sit for very long periods of time without flattening the battery.

Striker223

Great data and very consistent with what I saw on mine. All 5 cars I have in garages are on tenders though, I'm using the menards automated 2amp maintainers.

All of my cars have car side harnesses that are quick to plug in, I also always open the hoods anyway on the Audis to let heat out and on the truck to check hot idle oil PSI and fuel rail psi etc so they don't take extra steps.

JRA2000TL

I had issues of mine not starting with the first push of the button. 2nd time was fine--like right after you change the battery. When I first got the car, I had a bad habit of sitting in it playing with the options, testing the ML system out with different types of music, etc. I had it on accessory mode while doing that, and I'd subsequently shut it off for a few days. Once I quit doing that, I had no issues. I drive the car 2-3 days a week and the rest of the time it sits in the garage on a trickle charger. I can see how these cars could drain batteries quick, and my battery is less than 6 months old.

jmcraney

If your battery is good and you “drive it 2-3 days a week” you should not need to use a trickle charger. The definition of a “good” battery is a battery that has a fully-charged State-of-Charge greater than 75%.

Dean2

I agree. Tricklecharger is helpful for cars that might sit for longer periods of time, but should not be needed on ones used weekly and driven more than 20 minutes after startup. I have a neighbor that drives 2-3 miles each way, pretty much daily and rarely drives further. His battery needs help from an external charger every couple of weeks because the alternator can't replace the juice used to start the car in 3 miles.

BB9

2017 LS460 with Interstate battery, battery is about 3 years old. Was concerned about power drain myself at some point. Driving 4, sometimes 3 times per week, about 10 miles one way (about15-20 minutes), and then back. During winter couple of times voltage was dropping to about 11.7V over the weekend but car was always starting just fine. Every test I ran on the battery was showing battery as "healthy", probably dropping that low because it uses more juice to start when it is cold and not enough time to recharge. Had my car sitting under the tarp for 3 weeks and more at some point, when I came back car was hibernating (even keyless entry did not work until I opened it manually) and the battery was just fine. Never had a trickle charger. Few years ago bought one of these small booster packs "just in case" but never had to use it on my car. I think this car is smart enough to manage its own battery, as long as everything works as it should. For the long time storage trickle charger might be useful, but I would probably just disconnected the battery.