CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

12v battery reads good voltage but No AMPS

My battery voltage reads 12.7 volts stationary but when i try to start the vehicle it does want to turn over… I tried it with a new battery that reads 12.5 volts and it starts effortless.
How can i fix this problem?

Do a load test on the battery or bring it to a parts store and have them test it for free.

2 Likes

Classic sign of an old battery at the end of its useful life, it can have proper voltage but not be able to provide enough current. As @tcmichnorth says do a load test .

4 Likes

Leave the new battery in it.

6 Likes

Can you access the electrolyte? If so, you can measure its density with a hydrometer, a few $. Maybe the terminals need to be cleaned. Maybe a battery cable has broken. Maybe the alternator isn’t working and it isn’t getting a charge. Before you buy a new battery, take it in for a test. Even Walmart auto shops do this free.

1 Like

This is how batteries die internally. Some say due to sulfation of the plates inside… some say because of the acid… some say both

But they all call it the same thing… a dead battery. They dont last forever

2 Likes

My Dear Watson , I believe we can call that a Clue .

7 Likes

Measuring the specific gravity of the fluid in each cell is the only way to know the state of charge of each cell. It’s the tried and true method, for well over 100 years. Electronic measurements at the battery’s terminals cannot accomplish this.

Just have a conductance test performed on the battery

In a few seconds, you’ll know the condition of the battery.

BATTERY TEST RESULTS

I haven’t tested the electrolyte in a battery in over thirty years, or done a load test on a battery in over ten years.

Tester

2 Likes

You’re a working pro, with time constraints and the most modern instruments. I’m a retired DIYer with time to spare and reliable old tools. We both have something to offer here, for others to consider, or not.

1 Like

Based on what Tester said several years ago, I simply invested in a cheap version for maybe $60. Takes about 30 seconds to test a battery and I’ll check the cars and mower several or more times a year. May not be as accurate as the expensive equipment, but if you keep track of the readings you can definitely see when it’s time for replacement. So ya don’t have to spend a lot of money if you are a novice. Kinda like you don’t have to have a $200 socket set for a home owner.

I have not seen a modern battery, in over 20 years, where the electrolyte was accessible. I threw my hydrometer out probably ten years ago.

1 Like

I recently bought one for about same price as you. At first I was a little disappointed because it wasn’t as accurate. But once I go used to it I trust it more than my cheap load tester.

For the last couple decades or more, every one I’ve bought has two caps, each covering three cells. BITD they all had 6 caps. Either way, I can draw fluid out of each cell and test its state of charge by reading the scale on the float that’s inside the clear cylinder.

Tester

I’ve had several batteries fail within the warranty period. (Wal Mart, AutoZone) and they balked about replacing them because their conductance tester said the batteries were good. No way in hell were they good. “You just need to charge it a bit”.

Nope. They’ve been on the slow charge all night long and show 9 volts. Sitting there not connected to the car and voltage dropping like a rock without even applying a load such as a radio or park lamps.
Went through this just a month or so ago actually. When a battery goes from 12.6 volts to 7 volts in half an hour while sitting on a bench it has a problem.

Volts and amps do not necessarily correlate.

Most batteries that fail the performance test are fully charged when they come into the shop, dipping into the cells to check the specific gravity of the electrolyte is an unnecessary hazard.

We were using hand-held conductance testers in the 1990’s, they can be difficult to get a “failed” reading to get a warranty code for replacement.

For the last 15 years we have been using more involved test equipment for warranty requirements from the vehicle manufacture and Interstate Batteries. Many Manufactures require dealers to use the Midtronics GR8 to test batteries. This machine uses a combination of charge, load and conductance tests to check the battery.
Midtronics GR8 battery tester

The Midtronics GR8 is being phased out, replaced by more modern equipment, the Midtronics DCA-8000.

I bring a battery in to a parts store to be checked. When the kid hooked it up the conductance tester asked for CCA rating. He said that didn’t matter and used the default setting. I never used one of these before, but figured I wasted this trip. I ordered a conductance tester and checked this battery and it failed. Replaced the battery and problem solved.

All auto parts stores will test your battery for free. I will be willing to bet your battery is shot. . I will bet it’s over 5 years old. I will bet the water. In the battery is low. The easiest way to solve your problem with the least amount of aggravation is to Simply take the battery and have it tested and go from there. Now if the battery test good let us know and we’ll try and help you.