Is Your Battery Bad? A Simple Guide to Load Testing Batteries

Your battery may be suffering from a chemical issue if it’s having trouble producing electricity.

Getting the optimum life from a battery means sustaining it on a customary basis. You should detect the problems in your battery early and get them resolved quickly.

That’s why load testing batteries is of great significance. The process entails measuring the amperes generated by a battery. A battery in the auto needs to produce enough power to start the motor.

How to Load Testing Batteries

The battery of your vehicle isn’t demanding, and it’s often thought about after failing. Some amount of maintenance and care can prevent a sudden breakdown. The most accurate test involves inspecting the battery voltage and fluid condition.

The test requires a DC voltage meter and hydrometer, which you can access in local stores. If the trouble persists, there’re other troubleshooting steps to take. Are you wondering on whether your marine battery is packing up on you?

Here are a few tell-tale signs and a guide to help you through load testing batteries.

Tools You Need

For non-sealed battery, use a good temperature-compensating hydrometer. Use a digital voltmeter to test a sealed battery. It’s also used in troubleshooting an electrical or charging system.

It should have 0.5 percent accuracy or better. It’s not recommended to use analog voltmeters because they aren’t sufficiently accurate to measure the millivolt variations.

Inspect the Battery

Search for typical problems like broken / loose alternator belt, wet / dirty battery top, low electrolyte levels, and swollen / corroded cables. Also look for corroded battery posts/terminal mating surfaces, loose cable terminals, loose hold-down clamps, or a damaged / leaking battery case. 

Replace or repair such items as needed. Top up the battery fluid with distilled water. 

Recharge the Battery

Recharge it to 100 percent state-of-charge. What’s for a non-sealed battery with a difference of .030 (30 points) or more in gravity reading between the highest and lowest cell? Equalize the battery utilizing the manufacturer’s procedures.  

Remove the Surface Charge

If the surface charge isn’t removed, it makes a weak battery look good and vice versa. Remove it by permitting the battery to sit for 4 to 12 hours in a warm room. 

Measure the State-of-Charge

Use the recommended table to gauge the battery’s state-of-charge with the electrolyte temperature at 26.7 C (80 F). If the temperature isn’t 80 F, use the Temperature Compensation table to change specific gravity readings or open circuit voltage. 

The readings in a 100 percent state-of-charge battery differ by plate chemistry. Confirm the manufacturer’s specifications for a wholly charged battery. For non-sealed batteries, test the particular gravity in every cell using average cells readings and hydrometer. 

But with sealed batteries, use a digital voltmeter to get the open circuit voltage between the terminals.

Some batteries have built-in “Magic Eye” hydrometer which solely tests the state-of-charge in one of the six cells.

Whenever the built-in indicator is red, light yellow or clear, it’s an indication of a low electrolyte level. Non-sealed for such a case should be recharged and refilled before proceeding.

If it’s sealed one, replace the battery. Whenever the state-of-charge is smaller than 75% using a voltage test, specific gravity or the built-in hydrometer shows dark or white “bad,” recharge the battery before proceeding. Replace your battery in one or more instances below: 

  • If the battery shows .050 commonly expressed as 50 “points” or more gravity difference between the lowest and highest cell. The cells are weak or dead. Applying an equalizing charge can however correct this condition.
  • If the battery doesn’t recharge to a 75% state-of-charge level or more. Also, if the built-in hydrometer doesn’t indicate green or blue for “good” showing a 65 percent state-of-charge.
  • If a digital voltmeter shows 0 volts. It shows an open cell.
  • If the digital voltmeter shows 10.45 to 10.65 volts. It’s a probability of a shortened cell. The condition is due to plates touching, “treeing” between plates or sediment “mud” build-up.

Load Test the Battery

You can load test your car’s battery with a “good” built-in hydrometer indication or 75% state-of-charge. Use the following methods:

Use a battery load tester and apply the same load as half the CCA battery rating for 15 seconds. It’s the recommended method. 

By using a battery load tester, apply a similar load as half the auto’s CCA specification for 15 seconds. Stop the ignition and use the starter motor to switch on the engine for 15 seconds.

If the battery has a “good” built-in hydrometer sign or is fully charged, test the deep cycle battery capacity.

Apply a known load and measure the time it takes for battery discharge until it measures 10.5 volts. Use the usual discharge rate that lasts for 20 hours. 

For example:

With a battery that’s rated 80 ampere – hour, an average four amps load would discharge the battery in about 20 hours. Some new batteries take 50 charge/discharge “preconditioning” cycles before reaching their rated capacity. 

Depending on the application, completely charged batteries are “bad” when they have 80% or less of their first rated capacity.  

Bounce Back Test the Battery

Remove the load, wait for ten minutes, and measure the state-of-charge if the battery hasn’t passed the load test.

If it bounces to less than 75% state-of-charge 12.45 VDC / 1.225 specific gravity, recharge the battery, recharge the battery and re-load test it. Replace the battery if it bounces to less than 75 percent state-of-charge or fails the load test again. Such kind of a battery lacks the crucial CCA capacity. 

Recharge the Battery

Shortly, recharge the battery if it passes the load test. It prevents lead sulfation and restores it to maximum performance. 


Don’t allow small battery problems to go unnoticed. They cause bigger problems that finish up damaging the battery beyond repair. Load testing batteries helps you to know whether the battery has issues or whether it’s getting there. 

During the test, charge the battery fully to get an accurate reading. Count us for more reliable power and batteries.

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