My 93 has started draining batteries. What is a reasonable resistance measurement between positive and negative battery terminals, read with the battery removed? Mine is way high. This problem has eaten one good Interstate battery, and working on a second. While taking the car out for a short ride, a mile or 2 out, I got a ASR warning. Then it started flashing, then the instrument panel went dim, and all electric failed. No turn signal, can't roll the window down to give a hand signal. I had to make a turn. This is the kinda stuff that scares me in this car. Right now I've got the new battery on the trickle charger. Its taking a long time to charge. When I got ready to take it out, it was hard to crank. I am surprised that it ran the new battery down, so I may be looking at tracking down a short.

 

It clearly sounds like you have something that is not working quite the way GM wanted it too.

Your Alternator is common to both batteries. First I would check the alternator as it might be the root cause of all your trouble. The Alternator needs to be grounded so that is an easy check. Remove the new battery and charge it until it gasses (Boils) and then it will be close to fully charged. Reconnect your battery and start checking each fuse until you identify the one that has the electrical load on it. Harbor Freight makes a device that plugs into the fuse socket and tells you how much current is being used. You can do most of this with just a multi-meter.
By pulling each fuse and checking your battery voltage you might see find the load quickly. There are several ways but the best is to go fuse by fuse until you have the culprit identified.

With a fully charged battery you could measure the current being drawn by the car using a Multi-meter. The parasitic load is ~40 Ma or something like that. Measure the load at the battery using the Multi Meter's built in shunt as it should be less than 10 amps (I hope).

Using a Multi-meter check the OUTPUT from your alternator for Alternating Current (AC), there should be virtually none. If you find some AC mixed in there that would indicate that the Alternator has a bad diode in the diode bridge they use to take the AC and make it DC. Batteries DO NOT LIKE AC ripple! Your ECM and other equipment is safe from AC as the battery filters out a lot of it. The ECM should not go below a specific voltage or damage can occur.

If it is not the Alternator then the battery must have an internal short which is not easy to verify other than dealing with the symptoms. If a battery had a bad internal short it would go from 12 volts to a much lower voltage very quickly. I have seen this happen but the battery does not return to 12 volts after a internal short.

The more you can tell us about it the easier it is for us to solve for you! Sometimes it is a seat track motor that is stuck on due to a bad limit switch, or a power antenna motor that stays running.
Any modifications to your Corvette? Do you hear anything when the battery is connected versus disconnected?

 

Starter solenoid can be shorted as well. Great advice above👍

 

Great info. As most c4 readers know, the interior light stays on if the door is ajar, until the battery dies.
I think I found the problem. Air conditioning compressor! It reads almost a dead short. AND the short goes away on the positive negative post with the battery disconnected when unplugged.. That sucker will stay unplugged until I can get it to run and charge normally. I just hope I have not "killed" a new battery by reducing its voltage to something less then 12 volts, and have "trained" it that way, since its new not having much charge. I am not convinced I do not have another electrical problem. Why is it difficult to start? All I know is I never want to hear the word "opti" again!
Does anyone know what a compressor should have as a resistance reading? The thought of having to replace a compressor is very depressing. So expensive! I just got the thing to work. This electrical problem happened on the test drive for AC work. I rode around cool for a few miles!
Right now I have the battery charging on the charger. I have the option of borrowing the battery out of my wife's car this weekend to try in the vette.
Thanks for the input, I'll keep you posted.

 

You probably don't need a whole compressor, just the magnetic clutch portion on the front of the unit. That can be replaced with the right tools without having to depressurize the system or disturb the charge. If you take it to a local A/C shop they can do it. The car uses a Denso compressor that they will be able to get spares for pretty easily.

 

Would that account for the high current draw that loaded down the system?
Its unplugged at the compressor now.

 

Hard to say. But broken is broken so it needs to be replaced anyway according to your voltage / resistance test. Give it a shot....

 

I am very glad you found your Power drain!

The trick to saving your battery is to charge it completely with a real charger not a battery tender. You will need a few amps to get the electrolyte to gas. I would charge it up and keep it charged until your Corvette is feeling better with a new AC compressor.

Leaving a "partially charged" battery for any length of time is a bad idea. Always keep them charged up if you want to get a good life span out of the battery. I remove my batteries in the winter and keep them on a charging bench until I need them again. The inactivity of a few months can do some harm if the battery was not left completely charged. Batteries should get their maintenance at least once a year, unfortunately as long as they work they are ignored in a lot of cases.

 

Been through this myself (in July most recently.) In case you haven't actually found the cause: I found this useful: ( ). There's also this thread: https://www.corvetteforum.com/forums/c4-tech-performance/3332373-draining-battery-best-steps.html
best,
jerry

 

What is the difference in a real charger and a battery tender? Mine is a trickle charge. Its slow. 6-8 hours, maybe overnight. My thought is that is more like what a alternator or generator does,
And what is the yearly maintenance, you speak of?
I never have had a battery last very long with this car, because it doesn't get driven that much. Sometimes going a week or 2 between runs. I've used Diehard, and Interstates because they have good guarantees.

I really do want to get the car out of the hot sun, and back into the garage. So on friday, after a complete charge, I cranked her up. Was idling a little rough, but it was not yet warmed up.In the 30 sec., or so it took me to open wide the garage door it died, and would not crank. No clicking. No lights dimming. Nothing, as though the car was in drive. It wasn't. So there may be some credence in possible starter problems. I was gone yesterday, but have the battery charging now, with a plan to try to crank again after charging is complete and get her back in the garage.
THANKS!

 

You need a real battery charger to get the battery to full charge. Your tender only supplies 2 amps at best which is not enough to revive a dead battery. Get your alternator checked..

 

I had the newest Interstate battery charged and tested at the Chevy dealership. It is bad. This is the 2nd replacement, 3rd if you count the one that was in the car for 2 1/2 years.
But NO CHARGE on the instrument panel. Analog meter shows in the negative. Digital meter reads 12.4, and hard to read. Looks like a high probability of alternator problems.
I need a good battery to test with before I can proceed.

 

Hello there choopes!

Thank you 383vette, you said it well!
A battery tender is frequently less than 2 amps output and some are one amp output. The "better" battery tenders will taper the charge as the battery approaches the full point. The Harbor Freight unit I bought only put out 750 Ma but it cooked a new Interstate in less than three months as it had no tapering ability. It was very cheap and I had to replace a $160 battery because of it, not a good deal. I like to see at least 10 amps or more charging most automobile batteries but more current will do the job faster. I use a four stage charger that charges batteries even better as it has a different charging rate for each stage of charging the battery.

Lets say the new battery is 100 amp hours capacity, at 2 amps it would take over 50 hours to recharge a dead battery, a 1 amp charger would take 100 hours to fully recharge a dead battery. On a 100 amp hour battery you would want to charge it at 10 amps and it would be fully charged in hours not days.

What I mean when I refer to doing "Battery Maintenance" is the following.

1. At the end of the season I disconnect and remove the battery and clean the exterior of the battery but focus of the top of the battery. After it is cleaned I measure the open circuit voltage and record it.
2. I then open the battery up and check the electrolyte levels and add Distilled Water if it is low inside the battery. Many Flooded Lead Acid batteries have access ports or covers that can be removed to add electrolyte. If the battery has no way of adding water then I don't buy the battery as it is a disposable battery. I primarily use InterState Batteries and they frequently have covers you can remove to check the electrolyte.
3. Then I connect the battery to a charger capable of making the battery gas in a few hours (~10 amp charger). After gassing the battery is closed up and wiped down and put on a bench in my garage. Once a month I charge all the batteries on my bench to keep them "fully" charged. NOTE: FLA batteries have a issue with a higher self discharge rate so you want to monitor them closely. If the battery is allowed to go to a low state of charge then the battery will loose capacity if it stays there for any period of time.
4. The batteries are fully charged and then wiped clean and the terminal posts are cleaned with a wire brush.
5. The Battery connections in the Corvette are cleaned with wire brush and any corrosion is removed.
6. Re-Install the battery in the Corvette and secure the battery connectors on the battery.
7. Coat the terminals with Battery Grease to keep them from corroding while in the Corvette.

That is most of what I do for general "maintenance" of batteries. Be sure to have a fire extinguisher handy and some baking soda if needed. An Eye Wash Station is good to have when working with batteries. The electrolyte can blind you if it gets in your eye.
Any time I have a brand New battery I will charge it Fully before installing it in the Car. A lot of engines do not "fully" charge their batteries while in use in a car. Check your alternator for voltage output while you rev the engine a bit, it should get close to 14.5 normally. Also if you are having any kind of electrical issue I check the Alternator Output for any A.C. Noise or ripple in the background of the charge. To check you put the meter so it will measure A.C. Voltage and then check the output of the alternator using the engine for ground.

Check your Ground straps as they are vital to your Corvette working properly. I found one and after fixing it my antenna started working again.

Never leave any FLA battery partially charged as you will loose capacity quickly as a result.

Batteries charged on smaller chargers (less than 2 amps) can get "stratified" electrolyte and that is not a good thing for the battery either. If the electrolyte gets stratified the solution is a Good solid charge to get it gassing where it will break the stratification by mixing up the electrolyte. A stratified battery will act like it is normally charged until you try and load it up. Driving the Car with the battery is the best way to keep it from getting stratified. When FLA batteries get stratified they will show full voltage but when a load it attached it will drop the voltage fast and the battery capacity will be very limited. This is fairly common on batteries removed from their Cars for long periods and charged with a charger too small to really charge the battery. I rotate my four stage charger from battery to battery to ensure they are all at 100% or as close as they can be.

Regarding your no power at the Dashboard. Take a minute and measure the battery voltage, then measure the battery voltage at the fuse panel. They should be the same or VERY close. If not this would point to your fusible links and where they get power. I had a Corvette that sat for a while and when trying to start it again there was no power at the dashboard and barely 9 volts at the radio power wires. Near the battery area is a Post that is isolated from the chassis and it has a red wire that comes from the battery positive connector feeding 12 volts to the post. On the post were 7 fusible links that were corroded very badly. I spent some time cleaning them and afterwards I had 12.5 at the fuse panel like it was supposed to have. It was then that the Corvette came back to life. It is worth checking for corrosion IF you have a lower Battery voltage at the Fuse Panel.

 

Can you explain what you mean when you say it read as almost a dead short? What did you do?
I always try to learn more about electrical stuff when I can. This thread is very informative.

Thank you

 

I had some time today to investigate further.I got a new, higher amperage Interstate battery. The 3rd new one, I've been watching a bunch of you tube videos on parasitic drains and such. Here's what I found. The Alternator does not charge. Less the 12 volts on the cars digital meter. Analog meter is below the middle in the negative. No charging volts.
With everything off, and the battery removed. I measure between the positive terminal on the alternator and ground. I measure continuity (a complete circuit) in one direction, but not in the other. I repeated this test with the wire removed that is the permanent wire from the alternator to the battery. At this point I am thinking bad alternator, but the diodes are okay.
Next, onto the parasitic drain. I have never used my VOM to measure thru line current. I hooked up a jumper between the negative post connection, and the other to the battery negative terminal, so all current goes thru the meter, it is on the 10 amp scale, with the probe moved to that port. The first meter never read anything. Perhaps the fuse is blown. The second meter, my trusted Simpson 260, ran up around 4 amps then I realized the interior light had come on. Once it went out the meter dropped down to near 0. Milliamp range, and didn't come back.So did the parasitic drain fix itself? Amazing! Thesse things have a way of coming back later.
This all started when I was attempting to repair my A/C clutch. I found a bad diode in the bundle. THEN I started having the above described problem.So I cut open the bundle a 2nd time to look for stupid mistakes. Wires touching, or having come undone. I didn't find any.Still I have to wonder,.
I looks like whatever happened ate my alternator. Maybe it is time to get another. It seems there were 2 units. 120 amp, and 140. How can I tell what I need to order? Should I order a replacement, or is there something I overlooked to cover.
Thanks!

 

I would take the alternator off and take it to AutoZone or whatever parts store you have in your area and have it tested. You need to eliminate one item at a time when dealing with electrical problems. The car's computer is on all the time so there will always be some drain on the battery but it should be in milliamps I believe.