CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Battery Died Yet Car Still Started?

I was at a football tailgate and I had my tailgate open, doors open and the radio on, for probably 2 - 5 hours. I turned my car off, and later, when I went to start it, I think it started slowly, but it did start OK. I realized a short time later that my clock in the car was 75 minutes slow…like it had been “off” for over an hour. Why wasn’t my battery totally dead??? Can a battery get down low enough to disable the clock in the car, but yet have enough juice to start???

By turning off the power drain and waiting for a while, you gave the battery a chance to recover enough so it was able to start your car. The body control module may have sensed the voltage dropping when the load was draining the battery and cut power to the clock…

It’s certainly possible because I’ve seen this a few times. I once went to work in the cool morning air and the car would not start. Later in the afternoon…it started right up and I drove right down and bought a new battery. It had been slow starting for a while and I was just putting off the inevitable like most people do.

So based on this problem, does it mean my battery is “weak” and needs replacement? Is this something that can be checked by a shop? And I live in the Northeast, where temps will be dropping and I don’t want to find my car battery dead some cold, snowy morning !!!

Have your mechanic test the battery and he should be able to tell if it’s life is not long for this world.

Yosemite

Your battery can be load tested. Some clocks are sensitive to voltage drops. When the battery was going bad in my Ford Aerostar I owned some years back, the clock would sometimes reset itself to 12:00. The car would start, but it did crank slowly sometimes.
I have noticed that when I plug in the gadget that maintains 9 volts to keep the radio memory settings while I cleaned the battery terminals, the clock in my 2011 Sienna would lose time. Apparently, the clock needs its 12 volts to stay accurate.
Since you were tailgating and had your radio and interior lights on with the doors being opened for quite a stretch of time, you may want to petition the NCAA to speed up the length of the game by eliminating all the media timeouts. My wife and I went to a college football game this past Saturday and the media timeouts added an hour to the game. It’s even worse with basketball–the media timeouts destroy the momentum of the game.

You probably used the reserve capacity of the battery to start the car.

Reserve capacity is the amount of time the battery can operate the vehicles electrical systems when the charging system fails.

And as Caddyman stated, if the battery is in good condition and isn’t discharged too deep the battery can recover from the discharge if left sitting long enough.

Tester

Second the voltage sag as you cranked the engine with a week battery. And a sensitive clock electronics. The clock can be easily built to ride thru this but seams like they saved a few parts. If the batterys’ 4.or 5 ,6 years old get a new one., it’s time

@tjlamphere‌

If your battery is 4 or 5 years old, don’t bother testing it

Replace it now

A battery that was run down will recover a little bit if it sits for a while…Maybe enough to give you one start. Have you ever had a flashlight where the batteries were run down to a dim light. If you let it set for a few hours and you turn it back on, it will light brighter for a few seconds before dimming again. Thats what happened here. I would get the battery tested and if more than 5 years old replace it. Lead acid batteries do not like being run down anymore than 20% or can be damaged. To test a battery it should be resting for a few hours to get rid of any surface charge on it which can make a weak battery test good.

Car batteries are starting batteries and meant for short high discharge rates that start an engine.

I just replaced a 7 year old Wal Mart battery in my 89 Mustang GT…Car started without any problem in the morning., went into store for 30 minutes, came out and just that solenoid buzzing sound ( dead battery ). I have a manual tranny and luckily there was nobody parked in front of me. Had to use some muscle, and managed to get the car rolling, put in in 2nd gear and popped the clutch and she started…Off to buy a new battery. 7 years from a wal-mart battery, I can’t complain and only had a 2 year warranty. When they get past 4 or 5 years old can fail at anytime when you least expect it.

One thing I learned was if you start getting corrosion on your terminals its an early sign of battery doom. All it takes is one cell to get weak then the alternator tries to charge the battery at a higher current causing the cells to out gas and cause corrosion on the terminals.

Not sure what the 75 minute slow clock means, but I’d have the battery load tested. If it is already 5 years or older, I’d probably skip the load test and just buy a new battery.

I’d have to check my manual but some cars have a run down protection so that if you leave lights on etc. it will only allow it to run down to a point and then cut the power off. There would be enough left to start the car. Battery should be fully charged again and then watched to make sure it is still good.

Yeah, general motors definitely have had that feature for quite some time now

I’d have the battery tested after it was charged, either with a long drive at speed or with a charger.

run down protection
From the comments I see here, I'll bet some Porsche Boxster owners wish they had that feature!