How Can You Be Confident That A Used Battery Will Last?

Purchasing a used battery for your car can save you money or help you to get a dead car back on the road quickly, but it can also feel like a risk. How long will the battery last? Will you end up stranded again if it dies? Fortunately, you don't have to go into any battery purchase blind. Below you will find three options for testing a used battery before you hand over your hard-earned cash.

1. Perform a Simple Voltage Test

A "healthy" car battery should show a charge 12.6V or above. If you have access to a multimeter, then you can test the battery across its positive and negative terminals. When using your multimeter, be sure to set the mode to DC (direct current) and to use either the auto-ranging feature or a voltage range above 12V.

A voltage test only gives you a snapshot of the battery's current charge, but a battery that has entirely failed will often be unable to remain within its normal voltage range. If possible, perform your voltage test at least an hour after charging the battery. Since batteries in poor condition lose charge quickly, this should give you a decent indication of its ability to remain at the correct charge level.

2. Use a Car Battery Tester

Dedicated car battery testers don't cost much more than multimeters, and they can provide some additional information. Although buying a battery tester for a single used purchase doesn't make sense, these can be handy tools to have if you work with your car regularly. A battery tester can help to provide you with some additional information about the overall health of a battery.

Most battery testers will provide you with a cold-cranking amps (CCA) rating that can help you to judge the overall health of the battery. Your manufacturer should provide a CCA requirement for your car so that you can use this information to determine if the current state of a used battery is sufficient for your vehicle.

3. Test the Electrolyte Specific Gravity

Perhaps the most effective way to test a battery is by using a hydrometer to sample the specific gravity of the electrolyte. Although conducting this test is not difficult, it does require accessing the battery's electrolyte, and it can be dangerous if you do not know what you are doing. On the other hand, hydrometers are very cheap and can provide you with a good indication of a battery's health.

Although you can never be entirely sure about the state of any battery (new or used), performing at least one of these tests can give you the peace of mind you need to replace your battery with confidence.