The ideal way to charge a LiFePO4 battery is with a lithium iron phosphate battery charger, as it will be programmed with the appropriate voltage limits. Most lead-acid battery chargers will do the job just fine. AGM and GEL charge profiles typically fall within the voltage limits of a lithium iron phosphate battery. Wet lead-acid battery chargers tend to have a higher voltage limit, which may cause the Battery Management System (BMS) to go into protection mode. This won’t harm the battery; however, it may cause fault codes on the charger display.

The lithium battery charger can be split into different ways during the charging process. Firstly, the charger can steadily increase its voltage in order to keep the current flow constant. This is the first stage of the charging process – typically called the “bulk” charging stage. During this stage, the charger adjusts its applied voltage to deliver the maximum current to the battery.

For example, a 35 amp charger will deliver its maximum of 35 amps during this bulk charging stage, and the applied voltage will increase up to a maximum voltage, or “bulk voltage.”

Once the bulk voltage is reached, the charger enters a second stage, called the “absorption” charging stage. During absorption, the charger applies a constant voltage, called the “absorption voltage.” As the battery’s open-circuit voltage approaches the absorption voltage, the current flow steadily decreases down to zero.

At this point, the battery is fully charged. However, a lead-acid battery will rapidly lose charge when the charger is disconnected. So, instead of turning off, the battery charger enters a third stage called the “float” stage, in which the charger drops to a lower voltage and holds at that voltage. The point of this stage is to keep the battery topped off, and account for the fact that lead-acid batteries tend to drain, even when there is no load connected .

What If I Have More than One Battery to Recharge?

Many boats utilize more than one battery to help power everything from the starter to various quality-of-life accessories. Most marine battery rechargers can charge anywhere from one to six batteries.

You will most likely encounter the word “bank” when researching marine battery chargers. A “bank” is a single connection from the battery to the charger. This means if you have a six-bank charger, then it can simultaneously charge six batteries at once.