1972 Base 350, all stock. Went to start the car today after it sitting for about a month. Have it on Battery Tender which showed fully charged. It cranked several times at nornal speed then gradually slowed down until it just clicked. Voltage checks out at 12.4v. Battery is 6 years old. Car is only driven about once per month. I have no way that I know of to test amps, but I suspect something internal has gone bad and killed the amperage. Does that make sense?

 

IMO, it's a 6 year old battery. Replace it.

 

It didn't test OK at 12.4 volts. A fully charged battery should read 12.7 - 12.8 Volts.
Best way to test your battery is with a load tester. This way you can test cranking amps and voltage drop under load.
Most Automotive parts stores and Battery stores will test your battery for free.
Remove it and take it in with your other car and have it load tested.
At 6 years old be prepared to buy a new battery.

 

Agree with others above........its old, and if never used, its worse than if it was used regularly. And don't go down the rabbithole of buying expensive batteries......most batteries available to us here are made by the same few companies, with different labels on them.......i.e. they are all really the same battery. Forget Optima and all the other whiz bang marketing BS.

 

 

Go to YouTube for a non bias battery testing and interesting video.
The channel is called Project Farm. Best batteries?
Actually, the Optima Red and another brand come in the top two best.

 

Mine turned out to be he starter.........

 

It got deep discharged, and killed the ampacity, or the battery tender cooked it.

Like tires, a 6 year old battery owes you nothing. Go buy a new one.

 

I'd spring for a new one. Costco has great prices on their Interstate batteries.

 

I like Walmart. The last one I replaced was almost 8 years old.
And you can pick out the freshest. They have a round sticker on top with the month & year it was made..

 

I watched a fairly involved battery test on the big U, it showed Walmart batteries to be pretty damn good.
just saying

 

A typical battery tender connected to a Flooded Lead Acid battery is frequently not powerful enough to "gas" the battery. Battery Tenders instead can "Stratify" the electrolyte so some of the electrolyte can be fully charged and the rest of it not so well charged. This type of under charging frequently destroys or damages a battery. Most Flooded lead acid batteries need to get a good strong charge every so often to cause the electrolyte to gas and de-stratify. The batteries parts exposed to the more concentrated acid will wear the lead plates faster and the lower concentration acid will allow oxidation to occur. There are several variants of Battery Tenders out there. Some will work better than others depending on who made them. I bought a Battery tender that killed a brand new battery in one winter season as it boiled the battery dry, the charger was inexpensive but the lesson was not.

It is likely you might need a new battery after that experience. You might recover a bit of the original capacity if you put it on a 10-12 amp charger and let that baby howl. Charge it until the electrolyte boils or Gases off which occurs near full charge on most FLA Batteries.

IF you do need to replace your battery be sure to get one that lets you access the electrolyte. Some of the newer Lo/No/Less Maintenance batteries have made it virtually impossible to check the electrolyte. I am a big supporter of INTERSTATE Batteries as I tested and worked with batteries for many years. My success with Interstate has been good for the better part and I like being able to check and or add Distilled Water if needed. Most Flooded Lead Acid batteries use water and it is critical to be able to replenish it as it gets used up. Always charge a new battery up completely before installing it in the car.

On my Corvettes I pull the batteries out and bring them into my heated garage. I then clean the battery surfaces and wipe it clean to be sure not to get any crap into the cells. Once clean you pull the cap/covers off and verify the electrolyte levels in each of the six cells. After they are all topped off (to the FULL Mark) I attach them to a 10 amp charger and once a week I charge them for a day on a timer. When it warms up outdoors I clean the battery's terminal connections on the battery and on the car and then clean it's location. Last before reinstalling be sure to charge the battery to 15 volts I will clean the battery terminals and reconnect the battery. Once done I coat the tops of the terminals with battery grease as this helps keep the parts from oxidizing. At this point the battery should be ready for another season of use.

On a C3 I like to test the battery voltage at the engine by grounding the Black lead on the engine and the Red lead on the alternator output or Starter motor solenoid. Battery ground wires can get dirty connections just as fast as the long red cables can and do. While you are there be sure to check the output of the alternator for any Alternating Current getting through the diode bridge, AC voltage is not good on DC circuitry or accessories. Just measure the battery output using the A/C range to be sure that your alternator or doing it's job.

 

I would like to add that a Battery Tender does not need to be run 24 / 7.
I run two of them on two cars all winter. However, I only allow a half hour a day running time. That's all that most cars need.

A good battery monitor goes into a "stand-by mode once the battery no longer needs it. But is it really stand-by? A green light says its not changing so therefore the charger is not running right? Put your hand on it. Warm to the touch. Its still running.

Having said that, go to Walmart's electrical section. They have dial timer that's used to turn a light on / off in your home.
The dial has 48 positions, (half hour notches) for you to choose, time of day and for how long of activation.
Plug this timer into your garage wall outlet, plug your Battery Tender into the timer. Saves a lot of unnecessary wear & tear.