Battery drain from interior/aux power

GRAEYE

MEMBER
2000 FORD EXCURSION
6.8L
V10
2WD
AUTOMATIC
195,000 MILES

Having a consistent battery drain problem. It does not happen overnight or during operation, and the battery is able to take a charge. Interior gauge shows ~14v charging while running.

Battery is new enough to still be under warranty, and tested okay by auto shop.

If you leave the interior/aux power on while the vehicle is not running (such as by opening a door), it will drain the charged battery below the ability to crank the engine in under an hour. Maybe I'm wrong, but I don't think just the interior lighting would drain it that fast so I suspect something is contributing.

I've seen other posts here that mention checking for drain at specific relays and GEMS. If anyone has any likely suspects and could provide some details on what/how to test, I'd greatly appreciate it.

5 Replies

JONNYB1963

MECHANIC
252 POSTS

Good morning,

I just finished a similar issue on my Father-in-laws truck. (A 2000 F-250 V-10 Triton) He had a parasitic draw that was on all the time. For him it turned out to be the ACM module (the radio). But in his case it would take about 4 days to drain the battery.

I agree with you that you have some extra help in draining that battery at such a high rate.

What you have sounds a little different. From what you describe this only happens when you have the door open correct?

Jon

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Thursday, December 5th, 2019 AT 6:05 AM

GRAEYE

MEMBER
3 POSTS

Jon,

I haven't done any testing yet to isolate it to a specific thing. The vehicle is new to us so we've been doing little fixes and refreshes, often resulting in a door or two being open for a while. Key off, but either with a door open or opening and closing them frequently.

Nothing is turned on (radio, climate control, etc), but all of the interior and courtesy lights stay on for quite a while if you leave a door open. We recently left it parked for 2 days, after which it cranked fine. It's never been "dead" after sitting when we try it, only after we work on it.

Having the tailgate open for 2 hours and opening the front doors several times while working on it yesterday required we put it back on the battery charger before it would crank. It even did the bizarre behavior where the interior lights blink like hazard lights until you get more voltage into the system. A few minutes on the charger and it fired right up.

I don't know if it's something directly related to the lights, or just on a circuit that energizes at the same time or what.

Thanks

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Thursday, December 5th, 2019 AT 3:18 PM

JONNYB1963

MECHANIC
252 POSTS

Okay, so it sounds like a repeatable thing then for sure.

What you are going to need to do is exactly that. Isolate it.

The procedure I used with my in-laws vehicle is a little time consuming but it works.

What you will need is a multi-meter that can measure amperage. But Before you do this lets figure out approximately what sort of current draw you are looking at being that you can drain the battery in a matter of two hours.

What you need to figure this out is the specification of the battery. Most batteries come with a rating for CCA (Cold Cranking Amps) and a rating for Ah (Ampere Hours). Your Battery could have both listed but most commonly batteries just show their CCA on the label. If you are not able to find the Ah rating then just take the CCA and divide that by 7.25

Example. My Battery has 850 CCA. Therefore: 850 / 7.25 = 117 Ah which means that my battery can power a 10 Amp load for 11.7 hours. (117 / 10) So if I wanted to figure out how many amperes of load it would take to drain my battery in two hours then I just divide the Ah of the battery by the time required to drain the battery. (117 / 2) which would be 58.5 Amperes.

So for you, Find the Specs for your battery and do the same math. If you have the Amp Hour rating great! Then just divide that by 2 and there's your answer. If not then convert your CCA to Ah using the formula CCA / 7.25, and then divide that by 2 (hours) to get the size of the load that is draining your battery.

Once you determine the size of the load on the battery, you need to make sure you have a meter that can handle that sort of current. If the load is bigger than your meter can handle you may want to buy one of the clamp on current meters.

Let me know what you calculate the load to be or you can give me the specs and I'll do it for you if you wish.

Once we get that number I'll go further with the process because it differs depending on the type of meter we need to use.

Jon

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Friday, December 6th, 2019 AT 5:10 AM

GRAEYE

MEMBER
3 POSTS

Jon,

The current battery is a 650 CCA. We intend to replace it with an 850 when money permits, as other reading I've done suggests it's a good upgrade for these trucks with the V10 especially.

Your math above suggests a 45 ampere drain? Though since the battery isn't totally dead, I'd imagine it's less than that. But still substantial.

I had to order another clamp meter, I didn't have one that would do DC current. That puts us on hold until next week unfortunately. Should I be able to get a clamp reading from either the hot or ground to the battery and see draw? Could be interesting.

Thanks for your help thus far.

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Saturday, December 7th, 2019 AT 4:13 PM

KEN L

MASTER CERTIFIED MECHANIC
42,883 POSTS

Let's check the battery with this load test first.

https://www.2carpros.com/articles/car-battery-load-test

if it passes I have seen the GEM cause this issue lets unplug it and let the truck sit to see if it cranks over okay.

https://www.2carpros.com/articles/car-battery-dead-overnight

Check out the diagrams (below). Please let us know what you find. We are interested to see what it is.

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