OT: Car battery drain current

I can?t quote you a typical figure but do be aware that the initial discharge rate isn?t the same as the quiescent rate as modern power management systems ?load shed? after an initial period.

My motorhome?s central locking never worked after sitting for a period until I unlocked the doors manually, then it would work normally (always causing a bit of ?flat battery panic?).

Tim

stick your multimeter in line and tell us...

I?m not sure there is a typical value.

Our previous 4x4 was terrible, if you left it for more than few weeks the battery would be totally discharged. My wife?s car, which has a smaller capacity battery, is much better. Batter age etc wasn?t the issue. Even with a new battery in the 4x4 it made no difference and the one in my wife?s car is over 6 years old.

Assuming the battery is half decent, you should be able to leave it (even with the alarm on) for 2 to 3 weeks min. It was when we left ours for 5+ we had a problem.

How do you suggest he actually does that though Jim, talk him though the steps.

Cheers, T i m

Plug in a £5 12v battery powered OBD2 unit into the OBD2 socket under the dashboard....connect a multimeter set to current position between the battery post and the lead going to the battery....disconnect the OBD2 power lead read current......

I fitted a closed knife switch isolator on the -ve pole of the car battery and connected a 10 amp meter across the knife switch. I then opened the knife switch so the any residual current goes through the amp meter. The reading for my Golf R was 600ma.

It depends on how much of its electronics the car has that remains active when the car is sat on the drive longer term. Central locking receiver for a remote control for instance has to stay on power.

A working number is somewhere between 20mA at the most frugal end and commonly about 50mA (ie 1/50 to 1/20A). So a decent 40Ah battery will be dead in somewhere between 800-2000 hours if left untended (~a month).

I expect during lockdown plenty of people found this out the hard way.

The battery itself will very slowly self discharge with time and temperature even when it is not connected to anything. About 5% a month at UK ambient temperatures but faster when it is hot.

oh dear big mouth timmy has gone all quiet ....tee hee

does it not use hell of a lot more than that firing up from cold every time you reconnect ???..think that was the point timmy was trying to embarrass me with ....

only if you stop gaslighting timmy ....

I hear like lobsters they taste better that way ......

Wouldn't matter would it gasbagging Crazy Jim?

You are a bit sensitive / paranoid aren't you Crazy Jim? Actually, I was just asking the question as I wasn't sure how your very helpful initial advice, "stick your multimeter in line and tell us..." was going to work out for the OP?

Then you changed it with all the "Plug in a £5 12v battery powered OBD2 unit into the OBD2 socket under the dashboard....connect a multimeter set to current position between the battery post and the lead going to the battery....disconnect the OBD2 power lead read current......"?

I mean, does it have to be a £5 one? What current setting is the multimeter on (are we looking for amps or thousandths of an amp (I don't use mA, I don't do metric) etc)

totaly.....

Cheers, T i m

Now, who was it that started it this time Crazy Jim?

I was just asking a genuine question. I can't help it if you are paranoid and if you had a good answer in mind, there wouldn't have been an issue would there?

So, please stop gasbagging and actually try and help the OP?

Cheers, T i m

what part of that did you not understand?

well you have to explain to the hard of understanding ......

do you need to be spoon fed all the time timmy ? .....

in scotland it is totly....

well you asked me to explain then you complain.....no winning with you timmy boy .....

told you to stop gaslighting.......

genuine question my arse.....

I did

On Wed, 9 Sep 2020 10:13:45 +0100, "Jim GM4DHJ ..." snipped-for-privacy@ntlworld.com wrote: <snip>

Shame you couldn't have done it without the attitude and paranoia Crazy Jim. ;-(

Still not sure you have explained what this "12v battery powered OBD2 unit" is though? I mean, I have probably 6 ODB dongles, some bluetooth, some USB and one serial but none of them are '12V battery powered'.

My mate has a Suntune Diagnostic unit and that's charged / runs from a

So, what were you actually gasbagging about Crazy Jim?

Cheers, T i m

Mike McLeod explained :

My car - 20mA with an occasional flick higher every few seconds, as it does 'something'. I understand anything up to 60mA is considered normal, depending on equipment level.

Very difficult to measure, because disturbing connections can wake systems up. I was lucky - my main fuse box had an easy to remove bus bar link. I put my mA meter in parallel with the link, allowed the electronics to go into sleep mode, then removed the link without disturbing the meter.

I was suffering a too rapid flattening of the battery when parked for a period. I measured a worst case of 120mA, which was pulsing. I traced it to the voltage sensing relay for my towing socket, which was set to come on at too low a voltage. It was making, then as the voltage dropped it opened, volts drop would decrease and it would make again.

-rinse and repeat until the batteries charge was depleted.

jon explained :

That, if correct, is a rather serious discharge and would see the battery unable to crank in a week. I suspect you meant 60mA didn't you ?

You just get an ODB plug (cannibalising a cheap dongle may be one way) and wire a 12V battery across the relevant pins. Then disconnect and reconnect the battery while the ODB plug maintains the cars 12V supply. It's obvious.