confused about battery drain

[88911coupe]

My '88 is almost never driven (ac sucks...that's another story some have heard) so been keeping it on battery tender. However it seems to be losing charge faster than it should when I do drive it and leave it off the tender. Tell me if this sounds right, BTW I tested the draw and found it to be going back and forth (approx 1 second cycle) between 6 and 9 mA.
Sequence of events:
Car on charger several days. Last Saturday morning removed charger and tested battery, 12.55v. Started car and tested battery idling 14.04v, then drove car 40 minutes till tired of sweating my A$$ off, got home and tested battery at idle with radio and AC running. 13.1V.
Turned car off, sat 10 minutes tested @ 12.79v left car sitting in garage,no charger hooked up
plus about 24 hours 12.45v
plus another 24 hours 12.42
plus another 24 hours 12.39
Only thing I've added is a satellite radio receiver. I'm pretty sure I did the current test right after blowing several fuses...the draw seems to be well under anything that would be concerning. Battery is relatively new Interstate.
Does the drop in volts seem excessive?

Thanks and electronics are very confusing to me...

[The_PS]

Do the door-open switches work?

[tirwin]

I think anything under 20mA is probably normal. The cyclic alternating is curious but may be a red herring. A test would be to remove fuses one by one to see if you can isolate the cyclic source. The clock and the radio head unit are usually the only things drawing power on my ‘83.

Battery drain rate is affected by the battery temperature. I was dealing with this problem a long time ago and I found a calculation on how to figure out “normal” battery drain time. I can’t imagine that June in Dallas is a big problem though. So maybe you have a bad cell? You could take it to a local auto parts store and they will usually test the charging system.

Is it a traditional lead-acid or AGM?

[88911coupe]

I was assuming the small draw was the clock, but could probably narrow it down. However, even if I determine its the clock (or whatever) does it make sense the battery voltage would drop that much in 72 hours with 9 mA draw? That's what has me confused...is this indicating a battery that is not 100%? If it seems excessive I'll take it to Pep Boys where I bought it. Also, the switches seem to work fine as far as I can tell.

[creaturecat]

meter the fuses - to check the draw amount and the location
use this conversion table:

https://www.powerprobe.com/fuse-voltage-drop-charts

[911obgyn]

The cycle draw is the clock, charging system seems ok, the heat will lower voltage and amperage of alternator and voltage drop is not excessive. car should start at 11.5 V
You should drive it more

[Flojo]

what battery do you run (capacity)?
Some have such massive (diesel)batteries in their car, that the 70A/75A alternators don't really get a chance to load them beasts up. Especially when the cars sit more than gets driven and get driven only short stints and revved low.

[darrin]

Originally Posted by The_PS

Do the door-open switches work?

believe that what the_ps is referring to is whether your interior lights work when doors are open -- if not, this can result in a parasitic drain via the power window circuit, as it stays energized (and pulling current) after the ignition's turned off but before a door is opened allowing the driver to close windows with door closed and key out.

If door switches don't work, then power window circuit will remain energized (you can always roll up/down windows with key out) - in my '86 targa, this would drain the battery to a point where it wouldn't start the car in about a week.

Easy to check/fix and, especially as our cars get older and the door switches get oxidized, an increasingly frequent occurrence.

[dan88911]

+1 0n the door switches, I had the same problem on my car I purchased a few yrs. ago.
It was low mileage garage queen.

[tirwin]

If the door switches aren’t working and the lights are staying on, then wouldn’t the power draw be much greater than 6-9 mA?

I suppose it’s worth asking if there are any LEDs installed?

[The_PS]

Originally Posted by tirwin

If the door switches aren’t working and the lights are staying on, then wouldn’t the power draw be much greater than 6-9 mA?

I suppose it’s worth asking if there are any LEDs installed?

The problem is the other way — the power window relay stays energized until the door opens. I always make sure my door light turns on and off when I park.

I got two dead batteries from this before I fixed it and two after I thought I fixed it.

Of course disconnecting the battery to measure for a parasitic drain also resets the relay.

[tirwin]

Gotcha.

[88911coupe]

I’ll have to check the lights. I keep them in the “off” setting since it’s too easy for them to be in the permanent on position and drain the battery? I’ve done that a few times. Still thinking the draw is so low that’s not the issue.

[911pcars]

You noted the voltage drop off in your original post, but at the time didn’t know whether it was caused by a parasitic current drain or a bad battery. Isolate possible causes. If parasitic current drain is within specs, have the battery load tested.

Or... disconnect battery from vehicle, then connect your charger at least overnight. Check open circuit voltage immediately after charging is complete (disconnected). Should be minimum 12.6 V. Wait one hour, then repeat voltage check. If voltage drops below 12.6, suspect a very borderline battery. Continued voltage reduction confirms a faulty battery.

Next comes the question of what battery to buy. Whatever it is, try for an AGM battery (sealed). A rotted out trunk pan is very NG.

Sherwood

[88911coupe]

Thanks Sherwood that’s the test I’ll do next. I’m 99% sure my current draw is fine and no point in wasting time there.

[kuba_kuba]

I had same symptoms - ended up being the door switch. Like The_PS said above, connecting a meter reset the relay so was unable to find it that way.

[kltarga72]

Plus 1 on what creaturecat suggested


My recent experience with battery drain was the recent installation of a new power antennae that has a live 12vdc wire that will lower the antennae after turning power off to the radio. I saw that I had 2.74 ma draw on the radio circuit, after beating on the antenna mast power box amperage dropped to .64ma. I also installed a battery cutoff switch. I think that half an amp is normal draw for a 1980 SC (clock)

Lash

[tmadden2]

Originally Posted by 88911coupe

I’ll have to check the lights. I keep them in the “off” setting since it’s too easy for them to be in the permanent on position and drain the battery? I’ve done that a few times. Still thinking the draw is so low that’s not the issue.

It's not necessarily that the lights are on. It's that the broken door switches haven't de-energized the power window relay that everything else on that circuit is tied into. There's another thread on here where someone measured the temperature of the relay behind the dash. Even though it had been sitting in the garage, it was up over 100° F because it was constantly energized.

[speedracer92]

Doesn’t sound like this is the issue, but my turn signal lever in the car (1987 Targa) was engaged down (as if i was turning left) and even with everything off, key out, etc. it drained the battery. Crazy and maybe not designed correctly but fuse measurement showed me what was happening. Just a though.

[The_PS]

Originally Posted by speedracer92

Doesn’t sound like this is the issue, but my turn signal lever in the car (1987 Targa) was engaged down (as if i was turning left) and even with everything off, key out, etc. it drained the battery. Crazy and maybe not designed correctly but fuse measurement showed me what was happening. Just a though.

That will turn on the left side parking lights. Right side lights up if you have the lever up.