Battery Charging Problem PacificBattery.com

One charger can charge multiple batteries and many of our manufacturers suggest how batteries a specific charger can charge at one time. This is TRUE, however there are some rules that must be followed in order to use one charger for multiple batteries.

1) All batteries must be like sizes. For example you should not mix a deep cycle marine battery with a starting automotive battery or an automotive battery with a motorcycle battery.

2) All batteries must be of the same design. There are several types of Lead Acid Batteries. Gel, Maintenance Free, AGM (Odyssey, Optima), and regular flooded (where you can add water to them.

3) All batteries must be "about" the same age. Older batteries will damage new batteries. The rule of thumb is they should have an age difference of no more then a couple months.

4) All batteries should be at an equal level of charge. It is best to charge each battery individually and make sure they are all equal and in good working condition. Otherwise, one battery may be overcharged.

The picture below illustrates how batteries must be hooked together in order to charge multiple 12 volt batteries. It is highly recommended that batteries be removed from the vehicles prior to multi battery charging. There are NO wiring harnesses that hook to the charger and then have multiple leads going to different batteries/vehicles. The wires shown in the picture between each battery are called "jumpers" and are available at most local Battery Shops which sell automotive batteries.

When you connect multiple batteries together as shown, it is call "parallel" charging and you are keeping the voltage the same. By hooking the batteries up as shown in the picture, you are maintaining 12 volts.

OUR OPINION

We are showing you this reference page out of customer demand for this information. We do not recommend charging multiple batteries in parallel. Although it can be done effectively if all the rules above are followed, however it is our experience that it is RARE to have all the same batteries, all the same age, and of all the same design. And if the rules are not met, a battery can be destroyed and/or the charger might become confused about what is hooked up to it.

Multi-Bank Chargers are good alternative. Each bank acts independently to charge one battery. So, a four (4) bank can charge four separate batteries. The problem is, multi-bank chargers are expensive and for example a four (4) bank charger can cost around $300. In our opinion, it is better to save money by purchasing four (4) separate chargers for less then $50 each ($200 total). Yes, the manufacturers say you can charge 4 or 10 batteries with their chargers, however it is more of a competitive statement to compete with other charger companies. They are all guilty of it. A smart charger hooked to one battery will always perform the way you expect.

WARNING

If you do not feel you completely understand this example of how to parallel charge batteries, we recommend you contact an experienced mechanic or automotive technician. This example/outline of how to charge batteries is given for reference only. Use the suggestions listed at your own risk. Batteries can be dangerous or deadly if mishandled or improperly charged or maintained. Always follow the directions, safety instructions and warnings of the battery manufacturer and/or charger manufacturer.

Special thanks to VDC Electronics (Maker of the Battery Minder) for providing much of the technical reference.

When you connect multiple batteries in parallel, connect the "+" (Pos.) of the first battery to the "+" (Pos.) of the second battery. Then connect the" -" (Neg.) of the first battery to the "-" (Neg.) of the second battery. The + of the first battery and the - of the first battery connect to the CHARGER if possible; otherwise, connect to the accessible battery.