Deep-Cycle Batteries for Boats and Motorhomes: Gel, AGM or Dual-Purpose
Leisure batteries power lights, fridges and electronics for hours at a time. Learn how to size one from your daily energy use and choose between gel, AGM and dual-purpose designs.
Work out your daily energy use
Multiply the power of each appliance by the hours it runs, add them up and divide by 12 to get amp-hours per day. Then add a margin of about 50 percent, because a lead-acid battery lasts longest when it is never fully drained.
Pro tip: Aim to use no more than half of a lead-acid battery's rated capacity between charges.
Choose the chemistry
AGM batteries are sealed, maintenance-free and accept higher charge currents. Gel batteries have excellent deep-cycle life but need a charger with a gel profile. Dual-purpose batteries can both start an engine and run loads, at the cost of being a compromise at each.
Check size, terminals and mounting
Compare the group size and the length, width and height with the battery compartment, and confirm the terminal type and position. On a boat, secure the battery firmly: vibration and movement damage plates and connections.
Pro tip: Leave a little room for ventilation and for cables to curve without strain.
Match the charging system
The alternator, mains charger and solar controller must all support the battery chemistry you choose. A wrong charging profile is the most common reason a good deep-cycle battery fails early.
Pro tip: Check the charger supports AGM or gel before you buy the battery.
Related questions
What do the Ah and A numbers mean?
Ah is the capacity: how much energy the battery stores. The A figure is the cold cranking current: how much power it can deliver to start the engine. Match or slightly exceed the original specification, and make sure the terminal layout and dimensions fit.
What should I do with my old battery?
Used batteries must be recycled responsibly. When we deliver a replacement we can collect the old battery at the same time; ask for this at checkout or contact support to arrange it.