Strange intermittent flat battery twice now during the daytime and not 1st thing in the morning. 

Car is regular use everyday. 

1st time was at a petrol station first crank was flat battery and second was just enough to get it started. 

 

2nd was yesterday after a 20 mile run turned car off and returned 1 minute later to a near dead battery. Tried maybe 3 times to start and it didn't. 

Voltage with a voltmeter was 10.41volts after the attempts to start. 

After starting battery voltage was 13.98 volts amd alternator was 14.12 volts. 

 

Anyhow started with a jump. Went to halfords and got a battery test in which battery was good. 

 

So confused because if the alternator is not right im sure it trips a warning light.  Does this just sound like a simple battery. Ive always had the battery go slowly and first signs would always be cold start problems, but after a run battery would be charging and would hold for a little while and not die immediately but this being intermittent has stumbled me 

 

Even this morning started first time 

Bad connections on battery terminal posts, bad earth strap connection from engine to body. a battery test would bypass a poor post connection.

11 hours ago, superbdreams said:

Bad connections on battery terminal posts, bad earth strap connection from engine to body. a battery test would bypass a poor post connection.

i have had this problem. The connections on the battery posts had loosened. Solved the problem that i was having. 

 

How old is the battery? normally only last between 3 and 5 years. 

Ok so had anotger flat today while filling up. I find its when i leave keys in ignition and or interior lights on. 

Jum started got home connected a voltmeter which has been on now for over an hour and reading 13.0volts.

Where is the earth strap? Did check and clean posts and connections into distribution box and apply vaseline to all exposed metal. 

 

Any advice before i go an order a new battery

10.41volts after repeated attempts sounds like a dead cell on the battery - 

 

New battery time me thinks.

 

Edited 17 March, 20215 yr by bigjohn

Intermittent short circuit cell

6 cells x 2.12v each which makes up 12.72v fully charged

One shorted cell, (5x 2.12v) is 10.6v which is equal what you have seen on the volt meter.

 

I guess you have seen that there is no apparent pattern to it failing. Sometimes just the heat soak from the engine will put enough extra curvature on the plate packs in the battery to trigger a defect to short. Others will be down to the load applied across the battery causing the short to appear, usually when asking the starter motor to operate.

 

If the battery is aged a few years and been discharged and rapid charged a few times, that can also create short circuits with internal deterioration.

 

New battery...

Thanks for that. Yes most likely but its such a strange one. Ive always had cold start failure as a sign that the  battery is going but not when its driving and starting fine. 

Even now its showing 12.9v after sitting for 2 hours.