Normal battery state? 30 November 2022 at 8:45AM in Motoring 4 replies 165 views

rickyroma

My old battery seemed to lose charge more than normal. Replaced with a new battery (which does seem better) but I'm a bit worried there may still be a drain on the battery. I'll give you a few readings and would appreciate any opinions on if it is normal before I pay out for a parasitic drain test.

40 min drive home from work.. 12.6v that evening.
24 hours later (no travel)  12.5v
12 hours later (no travel) 12.45v
Following this reading I made 2 really short trips yesterday.. Took a reading this morning and it's 12.35v

I know it's no longer fully charged but it still starts the car. There is lots of contradictory advice on the net of course if these readings are OK 
Thanks! 

FlaatusGoat

This is so easy to troubleshoot and for the avoidance of doubt just get a multimeter between the battery and the positive lead whilst parked up and see if there's any draw flowing through. Wrongly wired head units are notorious for creating a parasitic draw.

rickyroma

FlaatusGoat said:

This is so easy to troubleshoot and for the avoidance of doubt just get a multimeter between the battery and the positive lead whilst parked up and see if there's any draw flowing through. Wrongly wired head units are notorious for creating a parasitic draw.

I'm not very practical at all lol
What do you mean between the battery and the positive lead?  I'm measuring the voltage between the positive and negative terminals using a multimeter. 

facade

Battery terminal voltage does depend on temperature, but I can't find any data on it.

To measure the parasitic draw, you have to disconnect one lead- the earth will do, and is less risky.

Make sure all the doors are shut and the lights  and ignition are all turned off first. HAVE THE KEYS IN YOUR POCKET (I fitted a battery to a peugeot once, and on connecting, there was a clunk as all the doors locked- with the key in the ignition)

get your multimeter on the 20A range, and connect it between the battery terminal and the lead.

It should read 0.00 to 0.05 A.

If it reads more, don't panic leave the meter connected, go and have a nice cup of tea, and wait half an hour and check again.

Sometimes it takes the car a while to get the idea and go to sleep.

forgotmyname

How much load on the battery when testing the voltage?   Off load voltage is misleading..

I can connect 9 AAA batteries and you will get 13.5 volts but it will not start your car. It will probably power

a bulb for a second or so and then the voltage will plummet.