Greetings,
I have a daily-driver 2000 LX470 with 265k miles on it. I'm having some electrical gremlins on it that I can't figure out, so I'm going to try and document exactly what has happened below, if anyone can help me diagnose.
In August 2024, the alternator died on me, and it took out the battery with it. I replaced both, the alternator with a Bosch 100A off of RockAuto, and a 24F battery with a warranty from Walmart. Everything seemed to be working fine for a few months, and then in mid-November, I was running errands with it and it died on me. I drove to the grocery store, ran in for 10 minutes, and when I came out and put the key in, nothing. No lights, no starter, no trying to turn over. My wife drove out and try to jump me off of her car, but it didn't have enough juice. We left it for a day, and eventually a friend and I went out with his corvette and massive jumper cables, and got it to turn over (barely). As I drove it, I watched the voltage meter on the dash drop whenever I idled, so I drove it in 2nd gear to keep the RPMs up. When I got to my destination, I shifted into reverse to back into the parking spot, and the truck died on me in the split second it was idling. We had to jump it again to get it parked properly.
Knowing the battery was only ~3 months old, and it had a warranty, I took it back to Walmart to try and get a replacement, hoping that would be enough to at least get me all the way home, where I could properly diagnose. At first, Walmart wouldn't let me exchange the battery, because their tester said it was perfectly fine. The manager mentioned they could put in on their bigger, more comprehensive tester, and when they did, the battery failed the "charge acceptance" metric, while passing everything else. I haven't been able to determine exactly what the "charge acceptance" of a car battery is, but I'm assuming it would be the obvious culprit of the alternator not charging the battery. Anyways, I got the new battery, stuck it in the truck, and everything seemed good to go. The voltage was ~12.7 when truck was off, and ~14.2 when on, which told me the alternator was still doing its job.
Fast forward a month, and the new battery died again. Same symptoms as before. I had been driving the truck normally on/off over the holidays, drove it to work one morning, and when I put the key in at the end of the day to go home, nothing. The battery voltage was reading low (I don't remember the exact voltage, but it was below 12.5, which told me the battery was dead again). I borrowed a trickle charger from a friend, hooked the battery up to it overnight, and the next morning started the truck up fine on the newly recharged battery. I drove it around like this for a couple weeks, trickle charging the battery every now and then to keep it juiced. This Tuesday I drove it to and from work, and Wednesday morning, put the key in, and nothing. I measured the battery voltage, and it was reading 12.2, so definitely dead. When I got home in the evening, I measured it again after sitting all day, and the battery voltage was 12.06. I recharged the battery, and drove it to work Thursday, determined to figure out the issue.
My best guess was that some sort of parasitic draw on the battery was what caused it to drop voltage throughout the day, so at work, I hooked up a current meter and measured the draw from the battery when the car was off. I measured 15 mA of draw, which was all going to the ECU (I determined this by pulling fuses until the draw went to 0). 15 mA is a very reasonable amount of current draw, so it seems like a parasitic draw isn't the issue. The alternator is still delivering 14.2 volts to the battery posts when running, so that doesn't seem to be the culprit either. At this point, my thinking is that Walmart just makes a crappy battery, and I know that they sold me a 24F when the truck originally came with a 27F (most places don't carry a 27F anymore). I took the truck to a local Interstate batteries, since they carry a 27F, thinking that a larger battery might help? The technician there took a look under the hood, tested my battery, and said that the battery is completely fine (his machine didn't test for "charge acceptance," so there's a chance that this battery still has that issue). He confirmed that the alternator seemed to be functional as well. He suggested that it could be an ECU problem, where sometimes it doesn't initialize, and then it gets stuck in an diagnostic loop which drains the battery over time. I will test if this is the case by pulling the fuse next time I have the issue to reset the ECU, before the battery has a chanve to drain, and seeing if the truck starts normally.
So that's where I am today. When the battery is fully charged, the truck seems to be perfectly fine. All the voltages on the battery and alternator are good, and there doesn't seem to be a parasitic draw on the battery when off. But I know that in a few days/weeks, I'll go to put the key in, and nothing. Dead battery that's so dead it doesn't even try to turn the engine over.
So here are my few working theories:
1. The alternator is supplying the correct voltage, but the current it is delivering is incompatible with the battery (either too high or too low).
- I've read on another thread that the earlier LX470s came with a 80A alternator, so replacing it with one with too much current can cause issues?
2. Walmart batteries are crappy.
3. The ECU has an intermittent issue initializing.
4. There is a random/intermittent parasitic draw that only happens occasionally, so I'm not catching it.
Can anyone provide some guidance?
TL;DR
New battery and alternator in August, charging system looks good, but truck will randomly not start due to dead battery every few weeks/months
I have a daily-driver 2000 LX470 with 265k miles on it. I'm having some electrical gremlins on it that I can't figure out, so I'm going to try and document exactly what has happened below, if anyone can help me diagnose.
In August 2024, the alternator died on me, and it took out the battery with it. I replaced both, the alternator with a Bosch 100A off of RockAuto, and a 24F battery with a warranty from Walmart. Everything seemed to be working fine for a few months, and then in mid-November, I was running errands with it and it died on me. I drove to the grocery store, ran in for 10 minutes, and when I came out and put the key in, nothing. No lights, no starter, no trying to turn over. My wife drove out and try to jump me off of her car, but it didn't have enough juice. We left it for a day, and eventually a friend and I went out with his corvette and massive jumper cables, and got it to turn over (barely). As I drove it, I watched the voltage meter on the dash drop whenever I idled, so I drove it in 2nd gear to keep the RPMs up. When I got to my destination, I shifted into reverse to back into the parking spot, and the truck died on me in the split second it was idling. We had to jump it again to get it parked properly.
Knowing the battery was only ~3 months old, and it had a warranty, I took it back to Walmart to try and get a replacement, hoping that would be enough to at least get me all the way home, where I could properly diagnose. At first, Walmart wouldn't let me exchange the battery, because their tester said it was perfectly fine. The manager mentioned they could put in on their bigger, more comprehensive tester, and when they did, the battery failed the "charge acceptance" metric, while passing everything else. I haven't been able to determine exactly what the "charge acceptance" of a car battery is, but I'm assuming it would be the obvious culprit of the alternator not charging the battery. Anyways, I got the new battery, stuck it in the truck, and everything seemed good to go. The voltage was ~12.7 when truck was off, and ~14.2 when on, which told me the alternator was still doing its job.
Fast forward a month, and the new battery died again. Same symptoms as before. I had been driving the truck normally on/off over the holidays, drove it to work one morning, and when I put the key in at the end of the day to go home, nothing. The battery voltage was reading low (I don't remember the exact voltage, but it was below 12.5, which told me the battery was dead again). I borrowed a trickle charger from a friend, hooked the battery up to it overnight, and the next morning started the truck up fine on the newly recharged battery. I drove it around like this for a couple weeks, trickle charging the battery every now and then to keep it juiced. This Tuesday I drove it to and from work, and Wednesday morning, put the key in, and nothing. I measured the battery voltage, and it was reading 12.2, so definitely dead. When I got home in the evening, I measured it again after sitting all day, and the battery voltage was 12.06. I recharged the battery, and drove it to work Thursday, determined to figure out the issue.
My best guess was that some sort of parasitic draw on the battery was what caused it to drop voltage throughout the day, so at work, I hooked up a current meter and measured the draw from the battery when the car was off. I measured 15 mA of draw, which was all going to the ECU (I determined this by pulling fuses until the draw went to 0). 15 mA is a very reasonable amount of current draw, so it seems like a parasitic draw isn't the issue. The alternator is still delivering 14.2 volts to the battery posts when running, so that doesn't seem to be the culprit either. At this point, my thinking is that Walmart just makes a crappy battery, and I know that they sold me a 24F when the truck originally came with a 27F (most places don't carry a 27F anymore). I took the truck to a local Interstate batteries, since they carry a 27F, thinking that a larger battery might help? The technician there took a look under the hood, tested my battery, and said that the battery is completely fine (his machine didn't test for "charge acceptance," so there's a chance that this battery still has that issue). He confirmed that the alternator seemed to be functional as well. He suggested that it could be an ECU problem, where sometimes it doesn't initialize, and then it gets stuck in an diagnostic loop which drains the battery over time. I will test if this is the case by pulling the fuse next time I have the issue to reset the ECU, before the battery has a chanve to drain, and seeing if the truck starts normally.
So that's where I am today. When the battery is fully charged, the truck seems to be perfectly fine. All the voltages on the battery and alternator are good, and there doesn't seem to be a parasitic draw on the battery when off. But I know that in a few days/weeks, I'll go to put the key in, and nothing. Dead battery that's so dead it doesn't even try to turn the engine over.
So here are my few working theories:
1. The alternator is supplying the correct voltage, but the current it is delivering is incompatible with the battery (either too high or too low).
- I've read on another thread that the earlier LX470s came with a 80A alternator, so replacing it with one with too much current can cause issues?
2. Walmart batteries are crappy.
3. The ECU has an intermittent issue initializing.
4. There is a random/intermittent parasitic draw that only happens occasionally, so I'm not catching it.
Can anyone provide some guidance?
TL;DR
New battery and alternator in August, charging system looks good, but truck will randomly not start due to dead battery every few weeks/months
