Dead Battery. Alternator?

[396chevy]

Hello, I have a 2000 LS400 and this all started about a month ago. I left a dome light on all night and in the morning it would not start so I got a jump start and drove it for for about 17 hrs only shutting it off a few times. And all those time it started good. Anyway I got home and charged the battery put it in drove it around a bit parked it for a couple days and again it would not start, So I had the battery checked and it was shot. Ok so I changed the battery, correct size optima 750cca battery. Everything worked good for a while, But because I can I checked the charge of the battery 2 weeks later and it was at 75% charge {12.4V} so I charged it back up and drove it again. Ok so 2 weeks passed and it has a tough time starting this am, got it started drove it to advance auto, had them check the battery and alternator. Late I know but better late than never right?? anyway the battery was low very low 12.09V or like 35% charged and the alternator output no load was 14.08v and 11.1A and under load it was 14.11V and 10.3A the guy and his print out are telling me the charging system is fine. And there was no parasitic drain, the printout says 0.00A but a friend tested it with a fluke meter and got .006A I think, But he said that was totally fine. My question is whats going on? Shouldn't the alternator be putting out way more than 14.11 volts with a load and a mostly dead battery?? I figured I killed it driving back home a while ago, but the tests say otherwise?? I am charging the battery tonight and will have it rechecked tomorrow but I would still like your input. Thanks Pat

[landar]

Pat...I do not know how you are testing the battery and coming up with 12.4v and 75% charge. A 12v battery is fully charged when it has, well, 12v.

If you have the engine turned off and are checking the voltage, then anything around 12v is normal. Start it up and the alternator should charge it around

13.5 to 14v (+/-). You really do not want the charging to go much north of 14v or it will begin 'cooking' the cells by overcharging. More is not always better.

The charging voltage should hold fairly steady if the regulator is working as designed.

To get a feel for how the battery is doing, I sometimes check the voltage at the battery (w/o the engine running) and turn the headlights on. This puts a decent load

on the battery and it will drop down to 12v or perhaps a bit under (11.9v). What I am looking for is the droop over time. It should hold close to 12v for at least 10-15 minutes or more, depending upon size of battery, condition of battery and temperature. The voltage WILL steadily drop, one millivolt at a time but should not go under, say 11.5 volts over this time period. In other words, a good battery with the right capacity for your car should be able to start the engine even if the headlights are left on for 10 minutes.

Another thing to check are the battery connections themselves. Do the same test as above (engine off, headlights on). Move the voltmeter probes from directly on

the battery posts to directly on the cable clamps. There should NOT be any difference, otherwise you have a connection (resistance) issue that needs to be cleaned. And it does not take much resistance to impede flow to the starter when it is demanding over 100 amps at startup.

[oldskewel]

All your electrical tests (12V, 14V, 6 mA) sound just fine. Looking at the original post, it seems the problem is "it would not start so I got a jump start." Any more details on that? "Would not start" = slowly turns? completely dead? turns fine, but does not start? ???

I once had a problem with an Optima battery that tested all those tests just fine, but would intermittently fail to start. Completely dead when turning the key. Then, as soon as jumper cables were hooked up (like 15 seconds later), it would start just perfectly. After a lot of troubleshooting, it turned out to be a bad battery (even though it was pretty new, and my previous Optima lasted 10+ years).

Also - I completely agree with all of landar's advice as well - but add to not rule out the chance that a new battery can be intermittently bad.

[396chevy]

All your electrical tests (12V, 14V, 6 mA) sound just fine. Looking at the original post, it seems the problem is "it would not start so I got a jump start." Any more details on that? "Would not start" = slowly turns? completely dead? turns fine, but does not start? ???

I once had a problem with an Optima battery that tested all those tests just fine, but would intermittently fail to start. Completely dead when turning the key. Then, as soon as jumper cables were hooked up (like 15 seconds later), it would start just perfectly. After a lot of troubleshooting, it turned out to be a bad battery (even though it was pretty new, and my previous Optima lasted 10+ years).

Also - I completely agree with all of landar's advice as well - but add to not rule out the chance that a new battery can be intermittently bad.

Ok the first time it would not start was with a diffrent battery, and it would not turn over at all. And the % of charge goes as follows, 100=12.70 95=12.64 90=12.58 85=12.52 80=12.46 75=12.40 70=12.36 65=12.32 60=12.28 55=12.24 50=12.20 40=12.12 30=12.04 20=11.98 10=11.94

[curiousB]

I would measure battery at the posts (both DVM leads not black one to frame) with engine off and nothing turned on. Should be around 12.0 VDC

Then start engine. No electrical loads other than engine running. Measure battery exactly the same way. Should be around 13.3VDC.

Then start turning on electrical loads. High beams, rear defogger, wipers, A/C, A/C blower on high, audio, bun warmers, whatever you can load up the alternator with. Then check battery voltage. If it has dropped under 13V or worse still under 12 then you have a problem the battery isn’t being maintained by charging system.

The problem could be:

1) loose, corroded, or dirty connections at battery posts or alternator.

2) loose or slipping belt on alternator

3) faulty alternator (worm brushes, blown stator plate diodes, or faulty voltage regulator module)

[rickatups]

Hello, I have a 2000 LS400 and this all started about a month ago. I left a dome light on all night and in the morning it would not start so I got a jump start and drove it for for about 17 hrs only shutting it off a few times. And all those time it started good. Anyway I got home and charged the battery put it in drove it around a bit parked it for a couple days and again it would not start, So I had the battery checked and it was shot. Ok so I changed the battery, correct size optima 750cca battery. Everything worked good for a while, But because I can I checked the charge of the battery 2 weeks later and it was at 75% charge {12.4V} so I charged it back up and drove it again. Ok so 2 weeks passed and it has a tough time starting this am, got it started drove it to advance auto, had them check the battery and alternator. Late I know but better late than never right?? anyway the battery was low very low 12.09V or like 35% charged and the alternator output no load was 14.08v and 11.1A and under load it was 14.11V and 10.3A the guy and his print out are telling me the charging system is fine. And there was no parasitic drain, the printout says 0.00A but a friend tested it with a fluke meter and got .006A I think, But he said that was totally fine. My question is whats going on? Shouldn't the alternator be putting out way more than 14.11 volts with a load and a mostly dead battery?? I figured I killed it driving back home a while ago, but the tests say otherwise?? I am charging the battery tonight and will have it rechecked tomorrow but I would still like your input. Thanks Pat

I am curious to know the milage of your car? I have always thought that a Lexus Alternator can go about 140,000 miles .... just for peace-of-mind I changed mine out at about 120,000 miles .....

[396chevy]

Hello, I have a 2000 LS400 and this all started about a month ago. I left a dome light on all night and in the morning it would not start so I got a jump start and drove it for for about 17 hrs only shutting it off a few times. And all those time it started good. Anyway I got home and charged the battery put it in drove it around a bit parked it for a couple days and again it would not start, So I had the battery checked and it was shot. Ok so I changed the battery, correct size optima 750cca battery. Everything worked good for a while, But because I can I checked the charge of the battery 2 weeks later and it was at 75% charge {12.4V} so I charged it back up and drove it again. Ok so 2 weeks passed and it has a tough time starting this am, got it started drove it to advance auto, had them check the battery and alternator. Late I know but better late than never right?? anyway the battery was low very low 12.09V or like 35% charged and the alternator output no load was 14.08v and 11.1A and under load it was 14.11V and 10.3A the guy and his print out are telling me the charging system is fine. And there was no parasitic drain, the printout says 0.00A but a friend tested it with a fluke meter and got .006A I think, But he said that was totally fine. My question is whats going on? Shouldn't the alternator be putting out way more than 14.11 volts with a load and a mostly dead battery?? I figured I killed it driving back home a while ago, but the tests say otherwise?? I am charging the battery tonight and will have it rechecked tomorrow but I would still like your input. Thanks Pat

I am curious to know the mileage of your car? I have always thought that a Lexus Alternator can go about 140,000 miles .... just for peace-of-mind I changed mine out at about 120,000 miles .....

Well in that case it may be due, It has 198K miles, previous owner did everything at the Omaha Lexus dealer and from online records It doesn't look as if its ever been changed. I am borrowing my friend fluke 88 and will do the tests curiousb suggested. I assume the tests can be preformed at idle? Thanks again

[curiousB]

Yes, do tests as stated with engine off and then at idle.

I might add a conditional test to the list. If you find battery voltage close to 12 VDC (or worse below) with engine idling and all electrical items switched on try the following. Get someone to rev engine up a bit. Maybe to 2,000RPM but no more. See if that gets you to 13.3 volts. Remember to measure battery at the posts (+ve and -ve) and the same each test so the voltage numbers can be compared to each other. Be careful of moving items when probing around with a running engine.

My guess is under heavy load you will see voltage at post be at or below 12VDC suggesting the charging circuit isn't keeping up at higher loads. That can be a slipping serpentine belt causing alternator to no see proper rpms (belt would likely be squealing though), brushes in alternator worn/contaminated or spring no pressing then firm enough to slip ring, loose wiring at battery and or alternator limiting current, maybe a blown diode or two on the stator rectifier plate (not really replaceable, new alternator), or voltage regulator is faulty and not driving alternator field current properly to get desired power out. Since alternator is a one piece unit this boils down to belt, wiring, alternator. Wiring is just your time (no parts) so maybe check that first and make sure connections clean and tight.

If however you have 13.3VDC or so volts with everything running your charging system look good and it must be something going wrong. Perhaps a bad battery cell or a leakage current when car is switched off (slowly draining battery).

Start with the measurements and that will at least give you more clues/narrow down options to sort this out. This shouldn’t be too difficult to sort out.

[396chevy]

Yes, do tests as stated with engine off and then at idle.

I might add a conditional test to the list. If you find battery voltage close to 12 VDC (or worse below) with engine idling and all electrical items switched on try the following. Get someone to rev engine up a bit. Maybe to 2,000RPM but no more. See if that gets you to 13.3 volts. Remember to measure battery at the posts (+ve and -ve) and the same each test so the voltage numbers can be compared to each other. Be careful of moving items when probing around with a running engine.

My guess is under heavy load you will see voltage at post be at or below 12VDC suggesting the charging circuit isn't keeping up at higher loads. That can be a slipping serpentine belt causing alternator to no see proper rpms (belt would likely be squealing though), brushes in alternator worn/contaminated or spring no pressing then firm enough to slip ring, loose wiring at battery and or alternator limiting current, maybe a blown diode or two on the stator rectifier plate (not really replaceable, new alternator), or voltage regulator is faulty and not driving alternator field current properly to get desired power out. Since alternator is a one piece unit this boils down to belt, wiring, alternator. Wiring is just your time (no parts) so maybe check that first and make sure connections clean and tight.

If however you have 13.3VDC or so volts with everything running your charging system look good and it must be something going wrong. Perhaps a bad battery cell or a leakage current when car is switched off (slowly draining battery).

Start with the measurements and that will at least give you more clues/narrow down options to sort this out. This shouldn’t be too difficult to sort out.

Ok I tested as you suggested, car off battery hooked up 12.75V, car on at idle no load 14.04V, car on w/load 11.79V amd it looks like my power steering pump is leaking......

[curiousB]

OK looks like alternator unable to deliver enough current. If you see PS fluid on alternator that could explain problem. The PS fluid breaks down and contaminates the brushes. You might be able to clean it up and replace with new brushes. Failing that a rebuilt alternator. Your probably want to fix leak at the same time or it might just happen again.