Car had to be jumped twice in past week. New battery.

[latenitecorolla]

Hello all! This is my first post; I'm excited to join the community of Corolla drivers!


I have a mechanical question about what could be wrong with my 05 Corolla (50k miles).


8 days ago my car wouldn't start. So I jumped it, and found it odd, but it seemed to be running fine. So I kept driving it and for a week it worked fine. Then yesterday (a week later), it wouldn't start again. So again I jumped it, and again it has been running fine. Obviously, I'm concerned as to why this has happened twice in one week, and afraid it may happen again. I replaced the Battery with a new one from Advance Auto Parts about 6 months ago.


So I thought I'd start with the Battery or alternator. I took the car to the Advance Auto where I bought the Battery, and they tested the battery, alternator, and starter. They said the battery looked okay but was not fully charged. They suggested I leave it with them for two hours while they charge it, then they will test it again for a final reading. They had some machine hooked up to the car and had me rev the engine, turn on lights/highbeams, turn on heater, turn off lights and heater as part of the testing. They said the alternator was good, and the starter was reading 11, when it should normally read 12, but said 11 should still be enough so they didn't think that was the problem. I came back 2.5 hours later and they said the battery was now fully charged and tested good. As a result, they would not replace my battery under warranty, and said they couldn't do anything else.


So now I am with a car whose battery and alternator are 'perfect' with a slightly weak starter. Any ideas as to why the car needed to be jumped twice in the past week? I had thought it was the alternator which I figured would explain why the car worked for a week in between until the battery fully drained again. Could a weak starter be the reason the car wouldn't start? In other words, the battery was strong enough, but there just wasn't enough crank in the starter to get it to run? And then putting jumper cables on made the starter strong enough? Sorry for my rambling, I'm just a bit confused.


Thanks to everyone in advance!

[alan333]

Strange that the Battery "looked ok but wasn't fully charged".  If you regularly do short runs with the lights/heater/demister etc on then the battery won't get a chance to charge properly.  A rubbish quality Battery will exaggerate this.. Put a volt meter across your Battery after the car has sat overnight and check the voltage.  It should be about 14 volts.  If it's down towards 12 (or less) then the alternator isn't charging (or the engine wasn't running long enough yesterday to fully charge it), or the battery is rubbish, or there's a drain somewhere on your electrical system.  Test the volts again with the engine running and make sure it's around 14 volts or higher.

If you have decent voltage in your battery then your problem probably lies elsewhere, and your starter could be a likely culprit.  Does it normally turn the engine over quickly, or does it struggle?

 

[oldcodger]

First off, what is the makers name and code/type of Battery you have had fitted ?

Are you 100% sure everything is off when you leave the car, eg no interior or boot light left on ?

As Allan says checking the Battery voltage is the first step,  thought think he has got the overnight figure mixed up, with the car sat overnight when you measure the Battery voltage , car not running, it should be around 12.00 - 12.5v , while running at around 2000 rpm it should then show around 14.00 to 14.5v DC if the alternator is charging.

Plenty of basic meters around for less than a tenner http://www.maplin.co.uk/p/maplin-domestic-multimeter-including-battery-bulb-and-fuse-tester-n20ax

Getting one like the maplin meter that measures up to 10 DC Amps would be handy as again with everything switched off, you could check that there is no Unseen current drain from the batter

 

[TomdeGuerre]

When you're testing a Battery it's important to accurately read the figures, preferably to the 2nd decimal eg

11.9 v = 20% Battery efficiency

12.12v = 40% efficiency

12.3 = 60% efficiency

12.52 volts 80% efficiency

12.72 volts 100% efficiency

 

You just say the car wouldn't start, you don't exactly say whether the starter was turning it normally or very slowly, which was it?

 

11v is not extremely low for starter voltage while cranking a cold engine, I wouldn't worry about anything above 9.5. Nevertheless it's worth checking the starter leads, especially the earth for clean sound connection and no fraying of braided cable strands. 

 

If the electricians checked out the charging system and it seems OK then I'd agree with Alan and OC, either you're not doing enough running to compensate for heater, lights etc in winter time or you have something left on causing a current drain overnight. But checking for current drain is usually done routinely when checking a charging system, seen it often when a boot light or underbonnet light was being left on due to a faulty switch.