ESHeisler

2008 SC 430.....battery went dead, to zero. Got jumped. Went to dealer who sold me new battery. COSTLY! Drove 90 highway miles. Got home & put trickle charger on to "just see" what battery recorded. It was at 75%. Removed trickle charger. Checked again following morning & battery at 65%. Who can advise besides the dealership? HELP.

ShawnOk

iTrader: (1)

Could be an alternator problem. Either take it to AutoZone or O'Reilly and ask them to do a free diagnostic... or there's the layman's way: Get the car started, let it run for about 5-10 minutes, then remove the negative/ground/black cable from the negative battery terminal. If the engine dies on you, then it's the alternator. If it continues to run, then it's something else and try the free diagnostic test at one of the aforementioned.

SC43052

DO NOT FOLLOW THE ABOVE ADVISE!

NEVER DISCONNECT YOUR BATTERY WHILE THE ENGINE IS RUNNING. YOU RISK SERIOUS DAMAGE TO A MODERN CAR'S ELECTRONICS. THIS WORKED FINE 50 YEARS AGO. NOT TODAY

One of three situations exist:
1. The old battery was bad and the new one is also bad. Highly unlikely.
2. The alternator is defective and not charging the battery.
3. There is a parasitic drain of the battery once you turn the engine off. Because the battery measured 75% after using the battery charger, but then dropped to 65% by the following morning this is the likely culprit, but I would also be wary of the battery chargers accuracy in measuring a charge. Also, just after charging or driving the car the battery will hold a surface voltage which is greater than the actual charge of the battery. To get an accurate reading of the battery's voltage if you want to read it immediately after charging or driving turn on the high beam lights for 1 minute with the engine off. Alternately, let the battery sit for 30 minutes before measuring voltage.

You can either diagnose yourself with a multimeter or cigarette lighter voltmeter (handy because you can monitor voltage before starting, just after starting and while you drive), or take it to an auto store for a free test of your battery and alternator. The battery should measure 12.5-12.6V when fully charged and the system voltage should be 13.4V-14V when the engine is running for a healthy alternator.

If the battery and alternator are deemed good then you should be able to drive it for an hour or so to fully charge the battery. Again, after the engine is off for 30 minutes the battery should measure 12.5V-12.6V then let is sit as long as you can (ideally a day or two). If after the car has sat if you measure a decrease in the voltage then there is a short, or something is staying on and draining the battery while the car sits. Common suspects are any new add-on electronic devices like permanently wired radar detectors, stereo systems or lighting that were wired incorrectly.

Good luck.

ShawnOk

iTrader: (1)

No offense or patronizing tone intended, but the directions above were how my mechanic of 10 years diagnosed my problem being a battery issue vs alternator issue about 3k miles ago. It may be an archaic method, but it's what he did. No damage resulted, I guess, but as a fair measure best option is to get it properly diagnosed for free at any of the car parts stores.

SC43052

Likewise, no offense or patronizing tone intended, but doing the same incorrect thing for 10 years does not make your mechanic a good electrical diagnostician. He may very well be skilled in many areas and may be able to rebuild an engine blindfolded, but if he has disconnected batteries from running engines on modern cars he has also been flat out lucky. He may have learned this from an "old timer" mechanic but it can result in a very expensive electrical failure.

It is also not an in-depth or reliable assessment of an alternator's electrical health. The engine will continue to run if the alternator is outputting 11.5V, 12.2V, 12.8V or 13.5V when you disconnect the battery. Which voltage would be indicative of a healthy alternator?

The battery acts as a filter (almost like a surge protector) for the car electronics and soaks up voltage spikes and over voltages that are produced by the alternator. These voltage anomalies are not necessarily common in a healthy alternator, but the chance of their presence soars when an alternator's voltage regulator begins to fail. There is no more dangerous time to disconnect the battery then when the alternator is suspected of failing.

If you do this to a car from the 50s or 60s that had no engine control computer, power regulation computer, anti-theft computer, transmission control computer, dynamic stability control computer, GPS navigation computer, etc. there was nothing to be affected by a surge. Doing it at the wrong time on your SC430 can cost you thousands.

Ask a Lexus mechanic (not the service advisor) the next time you are at a dealership if that is a good practice and he will look at you like you have lost your mind.

Or you might reference the Lexus SC430 factory repair manual, section 19-2 Starting and Charging System, that states "Never disconnect the battery while the engine is running".

Further, google the phrase "Disconnect a car battery while the engine is running" and you can drill into the details.

Engaging in this practice will not guarantee damage, but it is definitely playing Russian roulette.

Harold57

I'd go and get the battery load tested at a parts store, you probably should charge it up first though. If it tests out fine, then you likely have a bad alternator. The chances of having two bad batteries in a row are pretty low, so I'd guess that you have a bad alternator or a really bad power connection somewhere.

mandyfig

First off welcome to CL.

So how did you check the battery charge level? Through your trickle charger?

Did you start it and did it run?

Did you use a multi-meter to see what voltage you see? A well charged battery will read 12.7 to 12.8 V. If reading 12.3 and below, it is discharged.

If engine is running, you should see 14V across the terminals.

Google on how to tell if the battery is charged or the alternator is charging properly...

Good luck.

kjcole

Also, if it is a Lexus replacement battery, check that all the cells were filled properly. At least, mine installed in 2008 is a maintenance-style battery