Battery drain test procedure question
 

This may be a dumb question, but I'll ask anyway. I think I may have a battery drain problem, so I want to test the amount of parasitic current flow in the car's electrical system. The procedure as I understand it is to disconnect the positive battery cable, and attach the positive (red) lead from an ammeter to the positive battery post, and the negative (black) ammeter lead to the battery cable I just removed. My ammeter only goes up to 250 mA, but my car violently pegs the needle, indicating I have a large leak.

However, here's my question. Since the X5's battery is located under the luggage area, I have to open the rear hatch to get to it. So, when I connect an ammeter across the battery post and lead as described above, doesn't that complete the circuit and attempt to engage all the interior lights that come on when you open the hatch? Or is the ammeter's internal resistance high enough to prevent that? If this is a problem, how does one actually test the current drain on a car such as the X5, whose battery is located in the interior of the vehicle? Thanks.

Hi there,not really the way it should be.
You have to put the multimeter's lead through the insulation and just after that remove the nut from the negative cable where it meets the chassis.
If you disconnect the battery and reconnect either putting the cable back or through the multimeter,the faulty module is gonna be reset and you won't find any draw signs.

diyanich,

Thanks for the quick reply, but I'm sorry, I don't follow what you're saying. Been a long week, and I'm pretty tired, which is probably contributing to my inability to comprehend...

Which insulation are you referring to? Where exactly do you connect the multimeter's lead after putting it through this insulation? And which lead are you referring to for this, the red or the black one? What do I do with the other lead while I'm doing this? And I don't understand the purpose of removing the nut from the negative cable where it meets the chassis. What do I do after removing this nut?

Obviously, I'm completely lost. Could you please go through what you're proposing step by step, assuming I'm a complete ignoramus (definitely not a bad assumption!)? It sounds like you know what you're talking about; I'd just like to be able to follow the procedure you're recommending. Thanks, and sorry for being so dense.

That's ok :)
Look through the vinyl coating on the cable ,so you can reach the copper core .
Does it make sense now?

OK, that answers my first question. So I understand I'm to connect the red lead of the ammeter to the copper core of the positive battery terminal. What exactly do I do with the other ammeter lead?

I'm gonna write up in the morning.

Perfect, thanks. I'm on my way to hitting the sack myself. Looking forward to your description. Thanks in advance for your help - I'm sure it will be helpful to others as well.

The problem is that you don't want to disconnect the battery for this test. You want to measure the current when you turn the key off, and then watch it over time, and see that it drops down as various modules go to sleep. Disconnecting the battery doesn't let you do this. Diyanich is saying to use the ammeter to keep the circuit connected. I would rather use an inductive (clamp-on) ammeter.

That one would go around the Positive cable I guess.

Hi Multibeemer,
So here the question: what are your symptoms ? Why you suspect that the parasitic draw is the case?
Could you describe a bit?

Well, it's kind of a long, and somewhat embarrassing, story; I'm not even sure I have a problem, but I want to be sure, as it's primarily my wife's car, and I don't want to have her left stranded. I'll try to make it as brief as possible:

1. About a week ago, battery goes stone dead. No start, no lights, radio, nothing. Battery is six months old.
2. Take battery to get tested. Putting out 8.45 volts in fully discharged state. Way below spec. Suspect bad battery.
3. Have it charged and re-tested. Tests good!
4. Put battery back, but suspecting it's still not good, I leave the negative cable disconnected. Take it back to Autozone the next day to have it tested again and they find it's only 53% charged. They test it again in this state, conclude it is indeed bad, and they give me a new one.
5. Here's the embarrassing part. I drive home with the slip-on seat heater on, and forget to turn it off when I get home. Car isn't driven the next two days. Next time I try to drive the car, it's stone dead again.
6. Hook up a 2-amp battery charger to the connections in the engine compartment, and leave it charging a good 14 hours, but the charger never indicates the battery is fully charged, so I'm concerned there may be a parasitic leak, and it wasn't just the left-on seat heater that caused the battery to discharge. Thus my thread asking how to test the amount of parasitic leakage.

So that's the story. I'm still very confused about the battery drain test procedure. I've read I need a larger (e.g. 10 amp max) ammeter. Why? Mine only goes up to 250 mA, but I've heard the spec for parasitic current is only about 35 mA. What's this inductive ammeter JCL recommends? Is it expensive? Is it something I could rent? How is it used? How do I get around the need to have all the doors closed when I do the test, and the need to let the car sit for 20 minutes after closing them? Do I have to get in the car, crawl in the back to disconnect the positive cable, sit in the car for 20 minutes, and then crawl back with my ammeter to do the test?

Is it really this complicated? Could somebody please reply with a simple, step-by-step procedure on how to do this? Thanks.

Well,in the first case was definitely the battery's fault,I think.
So yours is 4.4i which makes it a bigger battery and longer charging time,so by just calculating the charge time 14h x 2amps = 28 amps which is so low for a "stone dead" battery.

It's low charge for 150 amps battery.
A heating pad would drain it fast,some people here had a cell phone charger draining their batteries pretty fast.
Before further testing I would get the battery a long 12 amps charge for two nights,as electrician said to me,it won't hurt at all.
And just after you get your X running I would monitor the draw if I would get the flat battery again,but keep in mind,if you drive short distances,like when go shopping Stop Start stop start endlessly,battery won't get enough juice back since it uses A lot during the cracking 1.7 kW.

What you say makes sense. And I'm encouraged by the fact that my wife misunderstood my request not to drive the car until I was certain it didn't have a current leak, and drove it after it had charged for about 10 hours, and had no problems. This was on a short trip, on which she made several stops. So yes, I'll give it a good long charge, and then monitor the draw. Thanks.

In normal driving conditions your battery shouldn't get flat even in winter time,given that you're in Texas.I am in Canada and sub temps are had on the battery.I always check the battery with my technique may I say.While cranking check the lights ABS Brakes and DSC in the dash.Once I have a strong battery none of the lights comes while cranking,battery is OK with brake(red) and ABS(yellow) light coming on,and when I have all 3 of them coming I start to pay more attention since at that stage I hear the starter revs slower and one of those times I just plug the 2 amps overnight and I am back to brake (red) light alone,if I let it for another night I am back to no lights during start up,doesn't stay long like that as I drive short distances everyday,about 3 miles to work and back,so I get 4 cranks a day just for about 12 miles.
I did the draw test trice before and my draw was below 0.025 amps.
Charge it,drive it,don't leave any accessory on for days and I guess you'll be fine.
Keep posted.

When you are measuring current draw with an ammeter, using the two probes, you need to have it connected in series with the battery cable and the battery post (or wherever you can disconnect the battery). The trouble is that when you disconnect the battery, you reset various modules, so for this test you have to go from a state of having the battery connected, to having it connected only through the ammeter, without breaking the circuit at any time. To do that, you loosen the cable connection connection, put a jumper wire across the connection, and then remove the cable. The jumper wire completes the circuit, so the vehicle is still powered up (but the jumper wire can't handle much power, so don't try to start it). Now connect the ammeter in parallel with the jumper wire. It won't read anything yet. Now disconnect one end of the jumper wire. The ammeter remains as the only connection, all the current goes through the ammeter, and you can get an accurate current reading. Be careful, because you can damage your ammeter from too much current.

The alternative is an inductive ammeter. It has to be one that can read very low currents. It has a spring clip with a coil in it, which clamps around the battery cable, without disconnecting the cable. It is much easier to use. It costs less than one hour of diagnostic time at your dealer, ie $100 or so. You may be able to rent one, I am not sure.

Yes, you have to determine how you will read the ammeter with the doors all closed. You will be doing this over 20 minutes or so.