What Size Battery Charger Do I Need?

The size of battery charger you need will be determined by the chemistry and capacity of the battery you are charging, as well as the loads you would normally run while the charger is operating.

The larger your battery capacity is, the higher your recommended charge current will be. The ideal rate of charge will depend on your batteries specifications, which can usually be found listed on the side of the battery or in the owner's manual. For example, the 200 B-TEC lithium battery shown below lists a nominal charge current of between 40A and 100A.
Generally speaking, the ratio of charge to total capacity is around 20% for lead acid batteries and 30% for lithium batteries for maximum performance and lifespan. For example, a 40A charger would be optimal for a 200Ah lead-acid battery and a 60A charger would be ideal for a lithium battery of the same capacity. When comparing a charger's output to the maximum charge current, you should also consider the number of chargers you will be running. Most caravans and RVs have the ability to charge from multiple sources (vehicle, solar, and AC mains) and some of these might be operating at the same time. All Enerdrive chargers have an adjustable output and can be turned turned down to match a smaller battery if necessary. This allows you to purchase a larger charger at the start if you think that you might upgrade the size of your battery bank at a later date and saves you from buying an additional charger down the road.

The constant loads that your battery will be running will also be a factor in determining the size of charger you need. When a charger is operating, it will supply all of the DC loads first and then whatever is left over will charge the batteries. For example, if you are running a fridge and LED lights that consume 10A of power and you have a 20A battery charger installed, then 10A from the charger will supply the load first and the remaining 10A will charge the battery. If you know that you will be running a lot of constant loads while you are charging, you may want to consider choosing a higher output charger.