alternator fine, battery fine, but battery occasionally dead

MassiveJim · 31 May 2014 at 13:16

Missus has a 1.6 W reg focus.

The alternator and battery have both been tested and are fine, (It has in fact had a new battery and had that replaced under warranty just in case)

However occasionally the battery will be completely dead and the car will need jump starting I do not know what is causing it.
She is absolutely certain that nothing is being left on
headlights were off, radio switches off when you turn the car off, interior light is set to switch off when door is closed.

Something is obviously faulty somewhere but intermittently so the garage can't diagnose it.
It happened again today but the battery was so dead I couldn't bump start it (we live on a hill) I had to get my car and jump start it and it now works fine again

the last time this happened was probably 2 months ago, it has happened twice in a week before now.

generally speaking she does do mostly short runs in it and I wonder if that is related but it has been used recently on journeys over 20 minutes which should leave plenty of charge in the battery.

any ideas as I am pulling my hair out with it ?

related or not I do not know, when getting into the car today (with battery dead) there was a ticking noise coming from the fuse box area under the glovebox whilst the door was open, when shut the noise stopped and obviously once the car was running the noise was no longer there either.

MassiveJim · 31 May 2014 at 13:28

I have just found this article on google

http://www.moderntiredealer.com/art...intermittent-dead-battery-problem/page/2.aspx

replacing the alternator would be an expensive way to find out we were wrong in 3 months time

Terminal_Boy · 31 May 2014 at 13:49

Is the light inside the boot going out when you close it?

Have you fitted any aftermarket ICE which is fed direct from the battery?

MassiveJim · 31 May 2014 at 14:29

if it is the light in the boot it would be intermittent because this does not happen every time.

No aftermarket ice.

Scania · 31 May 2014 at 17:07

MassiveJim said:
generally speaking she does do mostly short runs in it and I wonder if that is related but it has been used recently on journeys over 20 minutes which should leave plenty of charge in the battery.

Its not uncommon for brand new (2014) plate trucks to flatten their battery's when used predominantly for short, local trips, I mention trucks as if something with as much battery power as an HGV can do this, its little surprise a car will too.

The solution, is to trickle charge the battery's overnight / when the trucks off road for a service or whatever occasionally, it restores the battery's back to a full charge state, something day to day use won't.

An occasional run of over say 20 minutes won't necessarily put any extra charge back in, an alternator maintains a charge level, it isn't a battery charger in itself as such.

Given the garage can't find a fault - and presuming they are competent! - I'd try giving the battery a trickle charge overnight, every few weeks, and see if the problem persists, I'd wager it won't.