Flat Battery

[rob1295]

My car battery keeps going flat over a couple of days. It starts straight away when I jump start tho. Does the battery recharge better at tick over or do the revs need to be high ??

[mxyzptlk]

Sounds like you need a new battery.
But maybe just needs a good 10 mile run out to give a good charge.
If that doesn't work see first line

[Old_Geezer]

Regardless you ought to get it checked. Sounds like it may need replacing.

I'd have thought the revs made minor difference, if the current flows it'd charge eventually. But I don't know for sure if tickover maximises the charge current. Maybe not.

[sunny-dave]

You will get a bit of charge at tickover (modern alternators are pretty good), but a decent run (an hour or more) with the revs at a higher level is probably needed if your battery is actually too flat to start the car.

If it then goes flat over a couple of days then either there is something left on which is draining the battery (internal light, boot light, radio?) or the battery is knacked and you are probably going to need a new battery.

[tonyav]

How old is the battery in your car ?.

[rob1295]

Thanks......got a new battery a couple of months ago, along with a new alternator - must have some thing left switched on somewhere, but can't find it

[sunny-dave]

Have your sunvisors got the illuminated mirrors - they are a bugger for staying lit & flattening the battery.

[malagabob]

Maybe you should get the alternator output checked at the same time as the battery.
If the alternator is not charging the battery. Even a new battery will go flat quickly.
Just starting the engine will drain a battery, coupled with lights heater wipers etc.

[tonyav]

So's the one in the glovebox dave.

[malagabob]

Just seen your reply so disregard alternator. But might be worth getting output checked.
I always put plenty of vaseline on battery terminals and terminal connections. Damp between terminals can and will drain battery

[dustypuss]

I’ve found using Vaseline makes it easier to start too ;-)

[chas2008]

batterys dont always charge straight away from start up, some vehicles have to hit certain revs before the battery actually starts charging, so short low speed jouneys can and do drain the battery.
Also the red light on the dash isnt like the old days it isnt a charging light its an ignition light so even if the red light is out it doesnt mean the battery is being charged.

[ummmm]

I was always told that after a jump start you should take it for a run down a dual carriageway/motorway. Things might have changed though.

[Hopkirk]

I had this with the MILs car, and narrowed it down to one faulty circuit.

I didn't have a meter, so just put a bulb between the battery and the connecting lead. The light stayed on, showing there was a continual flow of leccy.

I pulled each fuse in turn until the light went out, so I knew which one was doing it.

[Teddio]

It may be the light is staying on in the boot when you close it. Try removing the bulbs from the boot lights.