Choosing a marine battery charger
Marine Werks buying guide · Updated November 2026
An onboard charger plugs into shore power and brings every battery back to full while the boat sits. Three choices decide which one fits.
1. One output per battery
Count the batteries you want to charge, not the volts. A 24-volt trolling motor runs on two 12-volt batteries and a 36-volt motor on three; add the cranking battery and a 36-volt bass boat has four. A multi-bank charger has a separate output for each battery and charges each one on its own, so a full battery never holds back an empty one.
2. Enough amps
A common guideline is a charger that delivers about 10 to 20 percent of each battery's amp-hour capacity: roughly 10 to 20 amps per bank for a 100 amp-hour battery. More amps means a faster recharge between trips. Lithium batteries can usually take more current; follow the battery maker's limit.
3. Match the battery chemistry
- Flooded lead-acid, AGM and gel each need their own charge voltages. Good chargers let you select the type per bank.
- Lithium (LiFePO4) needs a charger with a lithium profile. Charging lithium on a lead-acid setting can leave it undercharged or trigger its protection.
- If you mix chemistries (for example an AGM starting battery with lithium trolling batteries), choose a charger that sets the profile per bank.
Features worth having
- Multi-stage charging (bulk, absorption, float) and a maintenance mode for winter storage.
- A sealed, waterproof case rated for engine compartments.
- A temperature sensor so charging adjusts in hot and cold weather.
- Status lights or an app so you can see each bank at a glance.
Installation
Mount the charger where it gets airflow, run the DC leads with the wire size the manual specifies, and fuse each positive lead close to its battery. Use a marine shore-power inlet or a dedicated cord rather than a household extension cord.
