Current drain - what is normal?

[jamesh764]

I've just replaced the battery (for the second time in a month) on a friend's Cerbera as it was so flat the car could not be jump started.

The alternator is charging enthusiastically (maybe a bit too enthusiastically - it measures 14.9 volts).

I've measured the current consumed by the car with everything switched off, and it is 0.2 amps. Therefore the 60 amp hour battery will be flat in a fortnight.

I know of a woman who used to leave her car (not a TVR) undriven for months at a time while she had intimiate relationships with men around the world, and the car would always start when she got home.

So my question is, does this Cerbera have something wrong with it, or do they all use that much power when they're not being used?

[ukkid35]

I'd start pulling out fuses and watching for the current drop. The Meta M99T helpfully specifies 'low current drain', rather than giving an actual figure, but I would suggest that anything over 40mA is completely absurd for anything manufactured in the last twenty years.

[Supateg]

Previous owner, told me If I leave the face on the head unit it drains the battery, (never used it anyway!)
I can leave mine for upto two weeks and there is still life in the battery. (The rear boot light has been disconnected at some point, not investigated it)

I have two identical Hondas one can be left over two weeks the other will be flat within two weeks, only difference is the alarm system and a tracker.

I'm afraid it's a case of seeing where the drain is coming from.

[aide]

If it's any help, while you're looking for the cause of the drain, I fitted a battery brain and an optima red top battery and have never had any issues, no matter how long I leave the car.
Any time I go down to the car, when I unlock it to enter, the window zooms down and the door snaps open.
(just remember that when fitting the battery brain don’t forget to connect the live input feed to it, I just used the feed that powers the stereo)
Best wishes
Aide

[jamesh764]

Thank you for all the replies so far.

We had an Alfa with the M99T alarm, and that was fine to leave for weeks without flattening the battery, so that would imply Meta is correct when they say the alarm has a "low current drain" (assuming it's not faulty of course).

I think I need to spend a morning pulling fuses to find out which circuit is doing the draining.

[Tanguero]

While the alarm its self may be low drain the door lock signal that the alarm uses to lock both doors is by enabling a positive voltage to the control box rather than disconnecting the opening circuit. When I was tracking down the high battery drain on mine, that seemed to be the culprit.
I don't have a cure for it and ended up just using an Optimate to keep the battery topped up if I was leaving it undriven for more than a couple of weeks.

[Mr Cerbera]

Sorry to be Mr. Dense
BUT
How does one measure the current draw on a car battery ?
I have a multimeter but have no idea how to measure anything but potential difference.

Any insults are welcome as long as they are wrapped in a thin layer of advice.

[WhyTwo]

This is something I've been puzzled by recently.

I replaced the battery in the spring. Over the summer my car was left for around 6 weeks without being on a trickle charger (I had nowhere to store it until I built my garage). When I went to use it after 6 weeks it started first time no problem.

I now have it on an Optima charger but forgot to plug it in a couple of weeks ago. The following day the battery was too flat to open the doors. The only difference I can think of is the temperature, it was a sub zero night. How could that have such an effect on the battery?

Oh and I leave it unlocked in my garage for fear of the alarm draining the battery

[Tanguero]

Mr Cerbera said:

Sorry to be Mr. Dense
BUT
How does one measure the current draw on a car battery ?
I have a multimeter but have no idea how to measure anything but potential difference.

Any insults are welcome as long as they are wrapped in a thin layer of advice.

Connect your meter in series with the battery with it set onto a suitable current measuring range. First though you want to make sure everything is switched off and doors are closed as the extra current to run the interior lights and windows may well be more than your meter can handle.

[Tarmacshredder]

Mine will just start after 3 weeks being stood but any more and it is flat and having read previous posts that seams about right. Having spent years dealing with alfas nearly all the gtv's fitted with a meta alarm have the same problem of battery drain after 2001 they are slightly better. I would say it is the alarm but also check after market stereos and amps aren't being powered continuously on the accessory power source as these can also flatten the battery quickly.

[fatjon]

It's the alarm box behind the helmet holder. I unplugged mine and the current drain dropped instantly from 200ma to zero. I replaced the whole kit and caboodle with a Viper system with electronic door and boot popping and a proximity detection system and the battery still lasts for months without charging, although I do tend to leave it on a timed trickle charge over the winter months when it gets no outings. It is ridiculous that a modern vehicle should be fitted out from new with an alarm that can kill a fully charged battery in less than a month. I'm guessing it was cheap.

[OutlawFlat4]

Tarmacshredder said:

Mine will just start after 3 weeks being stood but any more and it is flat and having read previous posts that seams about right. Having spent years dealing with alfas nearly all the gtv's fitted with a meta alarm have the same problem of battery drain after 2001 they are slightly better. I would say it is the alarm but also check after market stereos and amps aren't being powered continuously on the accessory power source as these can also flatten the battery quickly.

Could you elaborate on how to check for this pls. Im worried it is happening to me.

I swapped the old aftermarket head unit for a newer one, but same harness, and added an amp which switches on when the head unit is turned on - direct power feed from the battery.....

I sometime leave my car on an accumate, but not always and never had a flat battery before. Could be co incidence but I want to know for sure as my RedTop wont take charge so having to replace and dont want it to happen again or worry about having to permanently have it plugged in......