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Car battery drain, especially cars with GPS connected.

Car battery drain, especially cars with GPS connected.

Car battery drain, especially cars with GPS connected.

Suffering from a battery that deteriorates after a couple of days of inactivity to the point that it wont crank the engine? It is very hard to determine the battery drain with an inexpensive multimeter. If you try to determine the "resting" discharge current and the car has GPS permanently connected it will often blow the fuse in the multimeter when you connect the multimeter in the earth line (in series). Most inexpensive meters will have a 10 AMP maximum DC current with an internal shunt in the meter. My car is a 2005 Renault Laguna. The GPS appears to be continuously connected,(makes sense as the GPS is always ready to go when you set off, which means that it must draw current when the car is idle).It constantly blew the fuse when I attempted to measure the resting current. Probably due to the surge of current when the battery is connected to live circuits (GPS, memory etc). A lot goes on electricaly when you reconnect a car battery hence the spark.
If you connect the meter to the negative battery connector and connect the other meter lead to the actual battery terminal and carefully remove the battery connector while keeping the connector on the actual battery without disconnecting either wire, you will not get the car re-initialising and possibly blowing the fuse and you can read the steady current discharge rate of your car. I am not certain but from research have found that the resting current should be less than 10ma, some references said it should only be 3ma. Mine was reading 10 times that amount.

So, you need the positive meter lead to the removable negative battery wire and the negative meter lead to the negative battery post before you disconnect the negative terminal from the battery.The meter should be set at 10amp DC current before you start the process (usually a separate meter connection on the meter which will connect internally to the shunt inside the meter). You can then reduce the current setting on the meter to determine the drain.

It would be advisable to have some help when removing the negative connector from the battery as even a momentary disconnection will start the setup routine that happens when you reconnect a battery. You need an uninterrupted connection. So someone keeping the meter prod in contact with the lead negative post of the battery.

Obviously you can use this method for any battery drain problem. If anyone has any other thoughts on this please add to the discussion :)

http://www.popularmechanics.com/cars/how-to/a5859/... ....................... well worth a look.

RE: Car battery drain, especially cars with GPS connected.

There's another short circuit. Any drain from a GPS is to maintain the real-time clock that the GPS needs to determine which satellites will be visible and sync up with - this is in the milliamp range, much like the drain on a wristwatch battery.

One technique is to remove all the fuses from the fuse panel and disconnect the alternator. If the drain is not zero then it is a fault in the primary wiring. If it is zero, then put one fuse at a time back in.

On one car I had a failure in a brake light switch - it was a pressure switch on the brake line and would provide just enough current to kill the battery, but not enough to light the brake lights, just warm them up.

The biggest sparks will be generated by charging large capacitors. so maybe an audio amplifier that is always on.

RE: Car battery drain, especially cars with GPS connected.

Can only speak with any specifics per factory service manuals for Toyotas, from their factory service documentation but that might provide a feel for what may be typical for other cars.

Their specified maximum permissible parasitic draw should be no more than 50 milliamps.

Below are some measurements I did on one of my vehicles that shows the combined effect of the ECU & security computers in sleep mode and in active mode. These measurements were made after I discovered by accident that the driver's door dome light switch not only operates the dome light, but is also used to bring the Main ECU out of sleep mode into active mode in preparation for starting the vehicle and in the process does things like pre-positioning the Idle Air Valve on the throttle body.

The above measurements were made after I had parked the vehicle in the garage with all doors open (and all dome lights off) overnight with a fan outside the vehicle blowing air into the vehicle to dry it out after the wife had spilled a significant amount of water onto the carpet. Much to my surprise, the vehicle battery was pulled down by the ECU staying in active mode due to the driver door being open (and dome lights switched off), to the point it would not start the engine.

Regarding the inrush current after reconnecting the battery with the meter in series, which could be from a number of loads, one that may not be obvious is the use by some manufacturers of fairly large capacitors in the main airbag arming controller to store sufficient energy to be able to fire the airbags and seat belt tensioner system for some time after a collision as the vehicle battery/wiring located well forward in the engine compartment may be destroyed in the initial phases of a multi strike collision. In my Toyota this energy storage system is kept charged by the battery even with the vehicle off.

Maybe the above will provide some reference to what you should see in your measurements and also some not so obvious effect of the ECUs not going into sleep mode due to some issue in that area. Obviously factory service documentation on your vehicle would be the best bet for you to know what to expect. And as stated above pulling fuses is a good way to isolate down to he circuit causing the drain.

btw if you google "renault discharging battery" there are a huge number of posts on the subject..

RE: Car battery drain, especially cars with GPS connected.

Thanks guys :)

RE: Car battery drain, especially cars with GPS connected.

did the car just start doing this?

Simple Inability to hold a charge is a possible failure mode of a well used battery.

RE: Car battery drain, especially cars with GPS connected.

It`s a 3 month old battery after similar problems with the previous one and there is definitely too much current draining away when the car is not in use @Tmoose. I have disconnected the radio/6cd player/built in GPS system (one unit, standard equipment)and it is much better, time will tell. It`s a 2005 Initiale Laguna estate. I got it for a good price about 6 years ago, love the car. Still only 67k on it. Battery condition generally looks fine @IRstuff, just about 3 months old. I have just retired so my runs mostly tend to be a couple of miles which isn`t good. The model is infamous for electrical problems and I`ve had my share which I have managed to fix myself. I`ll let you know if I have any further news on it. At the moment, after disconnecting the GPS/CD/Radio it is livable with :) I generally find the radio etc a distraction anyway. Thanks for the info @Danee, really usefull.

RE: Car battery drain, especially cars with GPS connected.

I would think you could use a standard VOM to find the current draw of the radio/GPS without blowing a fuse. If the combo pulls enough to blow the VOM fuse, I'd say you've definitely found the issue.

Dan - Owner

RE: Car battery drain, especially cars with GPS connected.

If inrush current is blowing fuses in a multimeter you can simply short the multimeter probes when first connecting then remove the shorting link to measure steady state current.

je suis charlie

RE: Car battery drain, especially cars with GPS connected.

Since the battery is failing I'd look at the alternator/regulator not working. And buy a trickle charger.

RE: Car battery drain, especially cars with GPS connected.

Brilliant post @gruntguru, why didn`t I think of that, oldtimers setting in ;)

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