2018 Corolla, Battery or Alternator?

Aug 13, 2004
I recently had a dead battery and then a slow crank event, so I’m looking for troubleshooting suggestions and next steps. I think the battery is probably going bad, but I want to make sure the alternator seems OK. I got this car last fall with 27,000 miles, 33,000 on it now. The original battery is stamped 6/11/17, so it’s just over four years old. Cables were cleaned a couple months ago.

The car needed a jump after sitting at the airport for a week. I charged the battery at least partially the next day. It was fine for ten days. Then it cranked really slowly but started. Testing with a cheap digital voltmeter, after about an hour of idling and driving following the slow crank, gave the following results:

Battery: 12.76
Running, no accessories: 14.03 to 14.06
Running, with A/C and engine fan, lights, radio: 13.96 to 13.97
(Readings at the OBD port with the Torque app were 12.7, 14.1, and 13.9 to 14.0)

1) Does it look like the alternator is charging enough?

2) Would the on-car charging system test at a parts store tell me anything more about the alternator than my voltmeter did?

I just finished charging the battery, so I will probably have it load tested before doing anything else. Here are this morning’s numbers, after a full charge and two short trips:

Battery: 12.57
Running: 14.05-14.07
Running with accessories: 13.96-13.98

The long backstory:

The car wouldn’t start after a week parked at the airport. I might have left the light switch on, but I’m not really sure. Lights came on, and it tried but wouldn’t crank enough to start. A jump pack started it.

The next day, I put on my CTEK MXS 5.0 charger. Charging was interrupted twice, once because my wife had to go somewhere after four hours and then because of rain. The charger completed the Absorption cycle and was on Recondition both times. I couldn't charge again because it rained off and on for the next week.

Ten days later, my wife was out and called to say the car almost didn’t start again. She idled for about 30 minutes to charge the battery and then was able to stop and restart two or three times in 30 minutes of driving. When she got home, I did the voltmeter testing above and ran a full recondition cycle with the charger, about 8 hours.
Probably not alternator with only 33,000 miles on it. Batteries seem to last only 3–4 years these days and yours is 4 years old, so there you go.

If you keep trying to nurse this battery, jump it a lot, idle to charge it, etc., you can end up killing the alternator. Been there, done that. Get a battery now.
You never "nurse maid" a battery as it will effects other parts in the electrical system in the negative, replace it if after you charge it and load test it that it fails.
Date code stickers, bar codes , purchased dates, miles and hours use of a battery means nothing except for warranty and record purposes. Also the date code is generally different from the actual manufactured date which is code melted in the case of the battery.
^ what Nitro said. Starters go bad too when fed by a poor battery because they never get up to their rated speeds, and have several times the amps going through at a much lower voltage, which fries stuff.

Your car should fit a $55 value battery from walmart that will still be better constructed than the OE one.
My guess is the battery also, especially in your warmer climate.

Another possibility - maybe check for current leakage/parasitic drain??
The car needed a jump after sitting at the airport for a week.
Usually it's the battery in that case. A bad battery wont hold a charge very long and if not driven for a week it isn't being charged up by the alternator.
Thanks for the confirmation. I guess I was spoiled by the Silverado I bought new that went 9 years on the original battery. This was a fleet car from South Florida, so who knows how the battery was treated.
If it was from Florida, a place all the hotter, then all the more likely to be time for a new battery.
A bad or failing battery in most all cases can be charged and can hold close to 12 volts however a battery that is failing can not support the amps for the volts. That's why to test a battery it must first be charged to 12.5+ volts.
The location of operation of a vehicle (with exception to very extremes of cold) environment has only a small part to do with the longevity and health of a battery because the under hood high temperatures are more engine operating temperature and it is a semi enclosed operating environment.
A parasitic drain does not follow the line of described voltage issues.
The treatment of a battery in the OEM mounted location has more o do with the condition of the battery terminals and the ground cables for clean and secure. Naturally a dirty battery as well any electrical component can never be completely relied on for lasting its design life.
I'm tired of Johnson Controls batteries leaking from the caps and ruining my hold down brackets, and don't have any warehouse club memberships, so I'm looking East Penn batteries from NAPA.

Their lower-end Proform (65 mo pro rated/18 mo free replacement) has a bit better cranking and reserve specs than the Advance "silver" 2-year. Would I gain much with the more expensive NAPA Legend beyond 10 months of pro-rating and 3 lbs?

Both are available in town if the load test is a fail.
didnt make the warranty? if not its probably the battery. ive gotten good ones only last 2 years and a red duralast lasted 9. seems like the battery and id get it load tested.