Car battery

26 Mar 2008
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United Kingdom
Hi all,

I’m having a bit of a problem with my car battery at the moment.

Just after New Year I tried to start my car after not using if for a week and it being cold and the car really struggled to start. Anyway in the end I managed to start it and soon replaced the battery for peace of mind. It’s a 09 reg Astra and it was the original battery.

Moving on last Monday I accidently left the lights on for the day and ended up with a flat battery. After jump starting it seemed fine for the next week. I was doing about 70 motorway miles a day. However after Saturday of doing a number of very short trips and not using it Sunday it wouldn’t start yesterday, needed jump starting again. The engine was turning but by the sound of it without much power. The battery measured 12.6V so I expected it would start. Jump started it again and it seems ok doing daily 70 miles on the motorway. However I’m worried it won’t last a weekend again. Does it sound like it just need a good charge? I was expecting the motorway driving would charge it up. Also I though with it measuring 12.6V it should be ok?

Any help much appreciated!

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With the engine running, you should expect to see around 14.4V across the battery......if this is present, the battery will charge up in no time.
Measure the voltage again whilst shouldn't fall below 10v if the battery is good and charged.
John :)
Cheers for that. I measured the voltage with he engine running and that was as you suggested. I haven't yet been able too do test it when starting the engine as I didn't have anyone last night to watch the multi meter as I started the engine.

So it sounds like as long as I don't leave anything on again I should have no problems now! Hopefully!
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Just for info, in case the evil returns.....
Batteries can discharge internally if they are old or faulty. Test here is to disconnect it and see if it holds its charge, or get a motor factor to test it for you.
The battery can also discharge through the alternator if that's seen better days - through the diode pack to be precise. The test here is to leave the battery connected up, but disconnect the alternator at its terminals.
John :)
Someone said batteries never recharge fully after going flat unless trickle charged off the car
I don't know about that, but you don't have to run a battery flat many times to destroy it, car batteries are not meant to be deep cycled but to be recharged immediately the car is started, that way only a very small part of their capacity is used and under those conditions they will last a long time. If they are completely discharged more than about half a dozen times they will seriously degrade.

Take it to your local garage, they should have a device which does a "drop test" on the battery. This will tell you how the battery is performing under load. If you are a regular they may even do it for free.
If you go to Kwik Fit they're bound to tell you the battery's dead.... plus you need 4 new tyres
Shoot! They told me it was only 78.1%. Feeling cheated :eek:
They charge me £25 for MOT's - Kwik Fit is aal reet with me :mrgreen:
John :)
No point in getting a cheap MOT if the car is failed on purpose to sell new parts. I'd rather pay a fair price for a fair MOT
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