Battery drain
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1st Gear
Joined: May 2025
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Battery drain
Hi all. Completely new to corvette (and cars). I purchased an 82' crossfire engine last summer and its given me a lot of headaches. I've gotten a few of the issues taken care of but this battery drainage - i dont even know where to start.
It was kept on a tender all winter but its not holding a charge. It did the same thing last summer but we replaced the battery, hoping it would fix the issue and it did not. The guy I bought if off of did put in a new stereo so I am wondering if that is the issue but I don't know how to determine that. If it isn't the stereo, I dont even know where to begin. Any advice or help would be appreciated!
It was kept on a tender all winter but its not holding a charge. It did the same thing last summer but we replaced the battery, hoping it would fix the issue and it did not. The guy I bought if off of did put in a new stereo so I am wondering if that is the issue but I don't know how to determine that. If it isn't the stereo, I dont even know where to begin. Any advice or help would be appreciated!
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Common sources of power drains are:
1. bad diode in the alternator,
2. courtesy lamp dimmer module (if your year has that),
3. bad ignition module,
4. "other" stuff.
If you have a DVM with 10 amp current circuit, put DVM ammeter in series with the battery. Pull all the fuses, close the door and read the ammeter to see if you still have the drain. If so, you have a diode problem in the alternator or a weird short in the main wiring harness, somewhere.
If you do not have the drain, put one fuse back in at a time and check for drain again. Continue that process until you see the drain, again. The fault is in the circuit with the last installed fuse.
1. bad diode in the alternator,
2. courtesy lamp dimmer module (if your year has that),
3. bad ignition module,
4. "other" stuff.
If you have a DVM with 10 amp current circuit, put DVM ammeter in series with the battery. Pull all the fuses, close the door and read the ammeter to see if you still have the drain. If so, you have a diode problem in the alternator or a weird short in the main wiring harness, somewhere.
If you do not have the drain, put one fuse back in at a time and check for drain again. Continue that process until you see the drain, again. The fault is in the circuit with the last installed fuse.
Advanced
Joined: Sep 2021
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Folks that know more about 82s specifically will come along but start with the fuses. How fast does it drain down? Find fuse panel and pull one. Still go dead? Put it back in and try the next one. After you’ve eliminated all the fuses. Then come back and guys will tell you where to go next.
When I got my 72 it would drain in 2-3 days. Finally figured out it was my horn relay. Plastic ring in steering column disintegrated grounding horn. Previous owner unhooked horn wire. Car still ‘honking horn’ but since not hooked up I didnt know it was still sending power.
When I got my 72 it would drain in 2-3 days. Finally figured out it was my horn relay. Plastic ring in steering column disintegrated grounding horn. Previous owner unhooked horn wire. Car still ‘honking horn’ but since not hooked up I didnt know it was still sending power.
Race Director
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Seems nowadays the most common cause of battery drain by far is the above mentioned diode in the Alternator.
try unhooking the alternator. 1 plug with 2 wires and one nut with one heavy wire. Very easy to get to. Try unhooking it and wait 2 days.
try unhooking the alternator. 1 plug with 2 wires and one nut with one heavy wire. Very easy to get to. Try unhooking it and wait 2 days.
Race Director
Joined: Mar 2017
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From: Virginia
If you want the quickest, highest probability fix, it is this.
I'd also install a quick disconnect on the negative battery terminal.
BTW, what battery tender are you using? The alternator is likely the cause of the drain (if not, the fuse method will likely find it). But I'm surprised your battery died in one season, unless it is an older style tender that doesn't protect the battery properly.
Le Mans Master
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From: mount holly NC
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Safety Car
Joined: May 2001
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From: Fairfax Virginia
I had a Battery tender that would boil the batteries dry with no voltage regulation. Beware of the inexpensive battery chargers, there is a reason they are less expensive...
Harbor Freight sells a CEN-TECH 20 amp Circuit tester that plugs into the fuse socket. The display on the tester will show you what is going through the circuit. A very useful tool when looking at batteries being drained.
Harbor Freight sells a CEN-TECH 20 amp Circuit tester that plugs into the fuse socket. The display on the tester will show you what is going through the circuit. A very useful tool when looking at batteries being drained.
Melting Slicks
Joined: Apr 2023
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From: Poplar Bluff MO
I use CTEK battery maintainers for all my vehicles that are not daily drivers or if they will sit for a couple of weeks or more due to weather. I had a maintainer that would top off the battery then go to sleep and never wake up. Went through several batteries on my Goldwing before I figured out that issue by adding a volt meter to the battery so I could monitor it every time I walked by.
JT
JT
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Le Mans Master
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From: Cool Northern Michigan
Mapman has a great answer.
Consider a battery shut-off switch a temporary tool until repair is made. Or a seasonal tool, as in long-term storage.
I would not want to use one every time the car was taken out for a spin.
You should never have to disconnect the battery after every use. Ridiculous.
An OHM Meter tester will find a parasitic drain. Just remember to jamb something in the door / dome light switch to cancel that while working inside the car.
Consider a battery shut-off switch a temporary tool until repair is made. Or a seasonal tool, as in long-term storage.
I would not want to use one every time the car was taken out for a spin.
You should never have to disconnect the battery after every use. Ridiculous.
An OHM Meter tester will find a parasitic drain. Just remember to jamb something in the door / dome light switch to cancel that while working inside the car.
Pro
Joined: May 2019
Posts: 556
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From: Fountain Hills (Phoenix) AZ
Seems like I am always working on my C3.... doors open. Battery cutoff switch comes in pretty handy.
Also - I don't leave any of the cars in my garage with the batteries connected. All have cutout switches.
Yes, you need to find where the parasitic loss is. The switch obviously isn't a fix.
Also - I don't leave any of the cars in my garage with the batteries connected. All have cutout switches.
Yes, you need to find where the parasitic loss is. The switch obviously isn't a fix.
Melting Slicks
Joined: May 2021
Posts: 2,261
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From: Fleming Island, FL
YouTube has many videos on this subject. Key word "parasitic battery draw". Don't overlook the battery itself. They can self discharge in a few days too. Even if the battery is new.
Last edited by Fly skids up!; May 9, 2025 at 11:12 AM.
Safety Car
Joined: May 2001
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From: Fairfax Virginia
Tracing parasitic drains using the plain old Volt ohm meter made life a bit more challenging as well. I personally don't think that making/breaking the power connection so many times is a good thing to do to the electronics used in the vehicle. I have a Marine Circuit breaker near my battery to protect the system and occasional use as a on/off switch. Being installed in a Convertible I try to use the right grade of equipment that doesn't mind a bit of humidity or a touch of moisture.
Race Director
Joined: Mar 2017
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From: Virginia
Seems like I am always working on my C3.... doors open. Battery cutoff switch comes in pretty handy.
Also - I don't leave any of the cars in my garage with the batteries connected. All have cutout switches.
Yes, you need to find where the parasitic loss is. The switch obviously isn't a fix.
Also - I don't leave any of the cars in my garage with the batteries connected. All have cutout switches.
Yes, you need to find where the parasitic loss is. The switch obviously isn't a fix.
I bolded the key line here. I park nice cars outside, so there's room in the garage for cheap C3s with 45 y.o. wiring harnesses. The battery disconnect means I don't burn up batteries, my car, or my house.
By all means, find the issue, and address it (and the links above should give you everything you need), but don't let anyone talk you out of adding a battery quick disconnect and using it. If there is no energy in the harness, you are much less likely to start an unattended fire.
I have also cooked batteries on charge, so I don't do that unattended, ever. If I need to charge a battery, it gets pulled out of the car, and recharged on my bench while I'm there. If I were to ever decide I needed an unattended battery tender, I'd take the advice previously given, and connect it to a manual dial timer, so that it only charges 30 minutes a day.
Melting Slicks
Joined: May 2021
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From: Fleming Island, FL
Race Director
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Generally, I use a milli amp meter. Chasing a parasitic drain in a professional shop is always done with a milli amp meter.
modern vehicles all have some drain even when computers and systems have gone to sleep.
Even our old C3's have a normal amount of drain from the clock and radio memory. This is measured in milli amps.
At any rate, based on the nature of the OP's original question. I just assumed he wasn't extremely knowledgeable or owned many advanced tools. So I gave a answer that required little in the way of tools. And could likely help.
modern vehicles all have some drain even when computers and systems have gone to sleep.
Even our old C3's have a normal amount of drain from the clock and radio memory. This is measured in milli amps.
At any rate, based on the nature of the OP's original question. I just assumed he wasn't extremely knowledgeable or owned many advanced tools. So I gave a answer that required little in the way of tools. And could likely help.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
I can use an ammeter or an ohmmeter to find a current drain. Not sure how one would use a millivolt meter to identify the source of a significant current drain, though.
Care to enlighten us on the process, 4-vettes ?
Care to enlighten us on the process, 4-vettes ?
Race Director
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A volt meter? No I can't help you with that. As I said above milli amps.
Safety Car
Joined: May 2001
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From: Fairfax Virginia
A good Volt-ohm Multi meter can measure Milli-amps, some meters are extremely accurate. On my Fluke 88 I have three places to the right of the decimal point in the "hyper accuracy" mode and it is easy to measure tiny drains. It can monitor the battery in the Min-Max mode watching the battery voltage or the meter can be put in-line with the battery ground wire to measure the current being drawn by the various circuits. The better the meter the more accurate it can be.
With the battery being monitored, the loads can be detected easily, as the battery voltage changes right away and makes the meter beep.
With the battery being monitored, the loads can be detected easily, as the battery voltage changes right away and makes the meter beep.