C5 Battery Leak

lead shot

If you own a squeaky clean C5, you’re still likely concerned about an acidic force that could be slowly destroying your prized possession: Battery electrolytic acid leakage.

Any wet cell battery is subject to leakage and side terminal batteries have an additional burden of holding back liquid acid. The lead side terminal is bonded to the plastic case to prevent leaks, but rough handling can loosen the bond. Over-tightening the battery cable retaining bolt can also break the bond. If the battery cable retaining bolt is too long, it can crack the lead terminal and allow acid to flow out of the bolt threads. Overheating during battery charging can damage the case and start a leak. This will be evident when you notice the battery case bulging out on all four sides. Batter leak can occur at the seam where the top and outer case bond together. There are products that may stop the flow, but for how long?

Some battery manufacturers have paid for damages caused by leaking acid though it is difficult to pinpoint what caused the problem. Rough handling or poor construction? The concern is increased when a side terminal battery is in a C5 because it sits on top of some very important components. The acid has a tendency to flow along the battery cable that has the leaky terminal. In this case, damage may be occurring out of sight. Although all earlier Corvettes will incur damage from a leaking side terminal battery it is not as catastrophic. Since the leak is at the top side of the battery it requires more “slosh” to lower the acid level enough to damage the battery or affect battery performance. The battery is generally neglected unless it is causing an obvious problem, so the leak persists and slowly causes major damage.

I once heard a chilling story of a leaking battery in a C5 that resulted in a repair bill of approximately $8K. The acid destroyed multiple wire harnesses and the TAC (Throttle Actuator Control) module. I have dealt with many C5s that presented with A/C concerns and found no vacuum to operate the mode doors. Upon further inspection and testing, I found battery acid had destroyed the plastic vacuum lines that control the A/C system. In one case, battery acid was being drawn up the engine harness with engine vacuum. In all these cases the plastic vacuum line was replaced and any wire harness damage was minor and repairable. Even these repair bills were $400-800. Extensive damage is certainly possible if the problem is ignored until electrical components start to do peculiar things.

Enough with the dark side! As an owner, you can spot the problem and have it addressed before major damage occurs. If you find a white powdery film on the battery terminal retaining bolt or on the outside of the battery cable, you have an acid leak. In some cases, the terminal retaining bolt and cable is clean but there is an acid trail down the battery below the terminal. What do you do? Change to a top post? Installing a top post will obviously change the look and require a positive and negative battery cable change or cutting off the O.E. terminals and installing those hokey repair terminals.

If you are using an O.E. or aftermarket replacement battery, install a Battery Mat first (part # 171002) to soak up any acid that might leak. The Battery Mat is a treated fiber mat that will retain and neutralize the acid. You still have to keep an eye on the terminals for the white corrosive powder because it is warning you that most likely acid is permeating the battery cable and headed towards the starter.


This positive terminal retaining bolt is showing minor corrosion. This is the best time to catch a problem. The cable terminal is not corroded and replacing the retaining bolt will eliminate further corrosion. The part number for correct cable retaining bolts is 173028 for 1969-2004 Corvettes. Be sure to check the length of original bolt before putting the replacement in the battery.


With the battery tray removed, you can see the harnesses below the battery along with the PCM (Powertrain Control Module) and TAC module. If this area has had battery acid spillage, thoroughly mix some baking soda and water (small box + quart water) and pour the mixture over the entire area. Then hose it out with tap water. If the plastic looms are damaged, seek professional help. The wiring condition will need to be evaluated to see if it can be saved or if replacement is required.


These gray connectors are used to connect the various computers together and are located next to the battery, near the positive cable. Check all the gray connectors for damage. If they are intact, use the baking soda and water mixture here also. If the connectors are damaged, the terminals may also be damaged, so keep the water away from them until their condition is evaluated.


This battery terminal looks harmless but it is already showing signs of leakage. The shiny lead will be dull in short time once the acid takes over. Tiny droplets of acid are near the terminal and it appears that the top of the battery is not bonded properly to the case on this battery. Be wary of this area!

Story and photos courtesy Chris Petris

One thought to “C5 Battery Leak”

  1. Wow, I’ve been blowing F9 a lot. Battery corrosion was evident and cleaned but the search stopped on that line of thinking. Next procedure to be attempted was isolation of individual circuits. Fix was only temporary, approximately 150 miles later the problem reoccurred. That mileage was similar between shop visit 2 and 3 also. Nope, after visit 3, the shop drive tested 400 miles and no problem. They declared, “we fixed it”. and approximately .25 miles the check engine light came on. The car had sat on the dealers parking lot unattended for a week. By golly, I am almost $2000 in the rears and YOU have given me hope! Thank you, Thank you, thank you!

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