87 base... battery has low voltage after sitting for 3-5 days... can’t find a parasitic draw... so I unhooked negative cable... charged with my smart charger... when it went to charge/float mode my meter said 12.68 volts... after sitting unhooked for 8 hours it’s now at 12.62... load test says battery is ok... it’s about 4 years old.... I was thinking full charge should have been 13-13.5.... am I right and it’s time for a battery? Thanks...

 

Nope, 12.6 is normal at rest. 13.6-14.5 under charge.

No sure how you are load testing, but a battery can show a good resting voltage and still show crap underload.

 

I took it to an auto parts store and used the electronic battery tester... it was charged to 12.6 when I tested it....

 

Then your battery is good. If it starts out weak, it will flag needing charged. If it fails under load it will flag as bad.

 

The batteries used in our Corvettes were Flooded Lead Acid batteries and the cars charging system is designed for the FLA battery. The batteries I am speaking of are the FLA batteries as used by GM.

The "Open Circuit" voltage of your battery should be at or near 12.6 vdc after it has been fully charged and had a chance to rest. I just bought a new battery a few weeks ago and it sits at 12.65 when not connected to anything external. The minute you attach any Corvette it will go down a bit faster. Today's new Cars have a lot of accessories that require constant power and their batteries. My C3 will draw down the battery just running a quartz clock mechanism.

Battery companies don't like to talk about the "Self-discharge" rate that a battery has. Most batteries are Self-discharging VERY slowly initially in their lives but the self-discharge rate gets much higher as they cycle or age. The Chemistry used in batteries also determines the rate of self-discharge. The best technology currently available for an automotive application with a very low self-discharge issue would be the Absorbed Glass Matbatteries. AGM batteries are very similar to standard Auto batteries but in place of the liquid electrolyte they use glass mat (i.e. fiberglass) to suspend the electrolyte. The electrolyte is thickened and applied to the Glass mat where it does it's job. AGM batteries are great because you "can" mount them on their sides or whatever. (Please Don't) The bad thing about them is that they require specialized charging because they have the potential of being overcharged by the FLA Alternators we have in our Corvettes. In case of an overcharge they become pressurized and this forces the relief valve to open dumping the excessive gas. AGM batteries are not keen on being overcharged very often...

The Self-Discharge rate of most older FLA batteries continues to get worse as it ages and eventually it won't supply it's load so it is replaced. Sometimes a battery can "short out" internally and frequently the get real hot real fast and then can explode. I have seen car batteries do this in their engine bay, it is not pretty.

One of the best parts of having a Flooded lead Acid battery is we can help it last longer with a bit of effort. I pull mine out and put them on a charger bench. I clean the surface and the connections and then I open the battery and top off the electrolyte. After cleaning up and filling the battery I then charge it fully. I use a special four stage charger but most good chargers will get the electrolyte to start to bubble or "Gas". After the charge the battery is kept topped off once a week until I do everything all over during the battery re-installation. Clean the terminals before re-installing the battery and you are assured another good season of enjoying your Beautiful Corvette.

Most Batteries in Cars are very "shallow cycled", what I mean is you pull some current starting it and from then on the battery is receiving some current which replaces what was used. The battery discharges a short time and gets a long re-charge so you are only using a very small amount or power from the battery and then just charging it. This is what uses the water in our electrolyte, the constant charging of the battery. Thank goodness they have a good alternator that "knows" when to stop. Bad alternators can boil a battery "Dry" as can a constant charger pumping out 1 amp 24/7 for a few weeks. Our alternators were designed with the proper settings for charging an "Average" Flooded Lead Acid battery.

There are folks trying to market automotive batteries made up of 18650 cells and they can be made to work for a car, our Car's are not designed for them and there starts the trouble. You will need a new alternator for each new technology battery to get maximum life out of that particular product.

For me and My Household we all use Interstate Flooded Lead Acid batteries in every vehicle except my RV which has a RV type of AGM battery for starting and ignition. I like the simplicity of Mr. Edison's Battery. I wish you could buy a Battery Jar and replace the plates as they wear out. Whomever thought of putting the battery in the engine bay was a battery salesman.

A Cool Battery is a Happy battery!
Reflective Heat Blankets to keep the heat out helps them last longer!

I installed batteries in the Middle East Deserts and they even lasted longer than expected!

 

How are you looking for the parasitic draw?

 

Buy the processes I have read on here, pulling fuses and relays while my meter is is series with the negative cable unhooked...

 

Hello there vyper202!

It sounds like you tested it in the correct fashion. A lot of Volt Ohm meters can measure up to 10 or even 20 amp loads. HF has a device that works very well, it is a device that plugs in place of the fuse and shows the current flowing on that line. I have two of them as they are handy. You don't need them if you have a good Volt Ohm meter and know how to use it. The HF device works well on the C4's and is very easy to use.

I have had a haunting parasitic draw on my C3 and it has challenged me. Turned out that the old amplifier for the stereo was on all the time and drawing a very small amount of current. I found it with the HF device as it would not show up with the battery connection method using a multi-meter. They are very inexpensive and work well. They are not as precise as the Fluke meter but hey, they helped me find a strange parasitic draw.

The C4's like my 1988 have a post near the battery where the fusible links get their power from. On my 1988 it is behind the battery under the side cover on a frame rail. The post will have a Red un-fused line coming from the battery positive that supplies the post with 12 Vdc. You could use your meter between them than find the parasitic draw on your Corvette. At least you can test each line individually and the Factory Service Manual, electrical supplement will show each fusible link and what it powers in the schematics.

Good Luck and Enjoy your Corvette!

 

Ok, what are you seeing for amps? My 96 draws 30mA when sitting, I assume and 87 will be about the same.

And did you pull fuses until you saw the amps drop? If so what fuse did you pull that stopped the parasitic draw? This will at least help identify what circuit branch the draw is happening on.

 

I have a question about "Battery Tenders" Do they actually extend the life of a FLA battery when the Vette is parked for long periods of time?

 

Hello Strick,

If you use a good quality battery tender that actually regulates based on voltage it will help make a Flooded Lead Acid battery last longer. There are plenty of less expensive Battery tenders that will boil your battery dry if you leave it on for more than a couple months.

This one thing most people seem to forget is that all FLA batteries have "Self Discharge" and as the battery gets older the self discharge rate increases. A new FLA battery has a moderately low self discharge but this also depends on the materials used to make the lead plates harder. In most automotive batteries (in the U.S.) it is Antimony and the more you use the harder the plates are, the more antimony in the plates will make the battery use more electrolyte. It is a vicious cycle.

The solution is to use other materials to make the plates hard enough to handle cycling. The German company VARTA makes a battery line that uses Selenium in place of antimony and those batteries have a reputation for not burning through the electrolyte and lasting longer. Selenium makes the plates hard and they last longer than a comparable lead antimony plate. I have seen their batteries go over 12 years in OEM usage.

When a battery is discharged the oxidation starts right away and it will take up all the discharged surfaces. If a battery is left at 50% for a while the capacity will be only 50% at best after a short period of time. When the battery uses some electrolyte and nobody replaces it you loose some of that capacity due to the oxidation of the plates which renders them useless. This is why I like the older style FLA batteries with easy access to the electrolyte. I will not buy any FLA where they try to make it "Maintenance Free". I service my batteries once a year and have found that to be enough for the limited use I subject my Corvettes to.

We need to be more proactive in taking care of our FLA batteries. Maintaining the electrolyte and the charge will help any FLA battery last longer.

 

Thanks CT. Looks like my alternator is not working as the voltage is 8-9 volts and going down when the engine is running. My "Battery Tender Brand" is flashing, alternating between red and green when it's hooked up. The alternator is the OEM one and might be failing. I guess it's time to bench test it.

 

Bench check -----it failed. Had to get another one.