Lead Acid Battery Charger FAQ

With so many devices that use lead acid batteries, locating the correct charger is essential to keep your gadgets running. Some things to keep in mind when looking for a charger is what type of battery you will be charging, size of the battery (not the physical size rather the Ah), and voltage. Selecting a battery tender to charge and maintain your sealed lead acid battery can be a daunting task. With this article, you will be able to successfully identify and locate a replacement for your battery.

How can I tell if my lead-acid battery is charged or not?

Lead acid batteries are made up of cells. Each cell is rated at approximately 2 volts. A fully charged lead acid battery cell is around 2.15 volts, and a fully discharged cell is 1.9 volts. So a 12V lead acid battery would measure at 12.9 volts or more when it is fully charged; and around 11.4 volts when fully discharged.

How Long Does it Take to Charge an SLA Battery?

Depending on the state of charge, this time frame will vary. You can approximate how long your lead acid battery will charge by dividing two numbers:

(Battery Capacity) / (Charger Current) = Hours

(Amp Hours) / (Amps) = Hours

Example: If you have a 30Ah battery and a 4 Amp charger, you would divide 30Ah by 4; (30 Ah) divided by (4 Amps) = 7.5 hours. So the estimated time for a 30 Amp-Hour battery using a 4 amp charger would be 7.5 hours.

What Charger Do I Select?

As indicated on our sealed lead acid FAQ page, selecting the correct battery charger will impact the performance and service life of a sealed lead acid (SLA) battery.

As a general rule of thumb when selecting a charger for a lead acid battery, match the voltage and use one that is no more than 20% of the capacity rating of the battery (at a 20hr. rate).

Example; to charge a 12 volt / 7.5Ah battery select a charger with a maximum charge output of 1.5 Amps (7.5 x 0.20 = 1.5).

Is There a Warranty on the Charger?

Depending on the model, warranties may be handled directly through the manufacturer. Please visit our lead acid charger warranty page for more information.

How Do I Connect the Battery to a Charger?

First make sure the battery voltage and charger voltage match. 

The positive charger output (RED) connects to the positive battery post.

The negative charger output (BLACK) connects to the negative battery post.

An easy way to remember is positive to positive, negative to negative.

How Do I Charge My Batteries that are Connected in Series/Parallel?

A battery pack that is connected together will have either a different voltage, amp hour capacity, or both. Since this changes the dynamics, please view our guide on connecting your sealed lead acid batteries together.