Yes I'm happy to leave the fuse out whilst I'm diagnosing the issue.  It's good to know the alarm won't be going off and annoying the neighbourhood, especially at night.

2 hours ago, Tog1966 said:

Haven't driven the car since the battery was replaced.

Was the old one professionally tested and what was the result.

51 minutes ago, KeithCheetham said:

Was the old one professionally tested and what was the result.

 

It's extremely difficult to accurately test lead acid batteries, but low voltage when fully charged is a certain sign of impending doom, a good battery will read 12.7V, a 50% life expired battery about 12.4V and 12.2V is in the realms a single chilly morning and your car wont start, not worth the inconvenience for the sake of a hundred quid.

17 hours ago, Tog1966 said:

Haven't driven the car since the battery was replaced, it read 12.74V out of the box yesterday, now showing around 12.45V having been in the car for just over 24 hours. 

That's a very big loss.

 

16 hours ago, Tog1966 said:

I wonder that if by trying to diagnose, fix and test the problem by constantly locking and unlocking the car plus starting it up a few times, whilst not actually having driven it anywhere to allow a recharge, I'm actually causing something of a drain myself!

Starting it up a few times whilst not actually driving it anywhere is never a great idea as starting the car is the biggest pull on the battery but if you are trying to diagnosis then you might need to which is why you need the battery in a good state of charge otherwise it will not help with the diagnosis and could actually hinder especially if you drain the battery more. and possibly create more problems.

 

ETA: One of the reasons I had to recharge my neighbour's battery was because he starts it then and leaves it idling on the hardstanding for a few minutes or sometimes drives it around the block, less than half a mile, and then leaves it for another week or two before starting it up again for a few minutes.

 

16 hours ago, Tog1966 said:

I'll give it a good run out tomorrow and check the state of the battery as soon as I'm back, then monitor it over the next 24-48 hours to see if it's draining.

A good run isn't always the best way to recharge the battery if the run isn't long enough and during that run you use a lot of electric load but it is better for the car than just sitting idling.  Recharging the battery fully off the car (especially as you have some sort of drain on the car it appears) would be best if the battery is too low, you could do that instead of or before your run tomorrow if you still need to go on the run.  Having a new fresh battery is certainly helpful now for use, diagnosis and recharging and gives more confidence.

 

Then its the usual look for the drain with a meter and pulling fuses one at a time or if you have access to a higher level scan tool you may be able to speed things up.

 

To give you an idea of how much you are losing so quickly figures from my neighbour's Ring battery charger/tester. -

 

12.7v - 100%

12.5v - 90%

12.4v - 80%

12.3V - 70%

12.2v - 60%

12.1v - 50%

11.9v - 40%

11.8v - 30%

11.6v - 20%

11.3v - 10%

Edited 7 April, 20224 yr by nta16

Charging a battery fully can be misleading with modern cars and the charging system of batteries and regeneration.   You might charge a battery as full as you can when disconnected from the car.  That is not fully charged though. 

The battery is not the problem. It never has been.

A battery in a low state of charge will not help particularly when looking for starting or electrical faults, you want to start with as much charge as possibly as the diagnostic work can and the drain on the car itself will deplete it's store.  Same with testing equipment, you don't want low battery on those that causes issues and prevents you from completing the job.  Same as starting out on a drive of unknown distance you'd check you'd got plenty of fuel.

 

IIRC Tog1966's car isn't start/stop so that's one thing out of the way, charging the battery fully is as can be done or measured with what is available and to start with the battery at measured full given the quick drain as seems to be now just makes sense to me - otherwise potentially the car is just parked up with the battery further draining, why not use this time to give extra reserve, a known starting point and confidence these give.  Just good preparation as the time and opportunity is available.