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Choosing a Marine Battery Charger

Keep your boat’s batteries at peak performance with these charger guidelines.

November 20, 2014
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Choosing a Marine Battery Charger

One of the most crucial aspects of your ship’s systems is maintaining healthy batteries. If they’re off, the performance of the electronics and electric appliances will suffer — if you’re lucky enough to start your engines. If you install a charger, follow the guidelines outlined by the American Boat and Yacht Council (ABYC) in section A-31. Also, heed this advice gleaned from Randy Wang of Powermania (powerma​niausa.com) on what to look for in a marine battery charger.

Size Matters
Choose a charger with a rated output (amperage) that’s about 10 to 15 percent of the combined batteries’ capacity (ampere-hour or Ah). So if you need to recharge two Group 27 batteries (2 x 105 Ah = 210 Ah), a rated 20-amp charger is a good fit.

1. Bank Notes
A typical dual-bank, 20-amp charger has a 10/10 per leg configuration. That is, each output is capped at 10 amps maximum. But if a boat has one small starter-cranking battery and a larger house battery, they won’t discharge at the same rate. A 10/10-amp charger will likely waste one leg’s 10-amp power in idle because the cranking battery charges quickly, while a depleted house battery can only be simultaneously charged at the maximum current of 10 amps. A “smart” charger automatically transfers the idle charging current to the battery that needs more power.

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2. Charge Rate
Theoretically, all 20-amp chargers should charge at the same rate, but they don’t. Many chargers lose output power (amps) as they heat up. For example, a 20-amp charger puts out 20 amps at first, but after 30 or 40 minutes into a recharge cycle, it gets warm and drops to 14 amps or lower. That would make it a “20A peak, 14A consistent” charger. A “20A-rated” charger consistently maintains 20 amps of output or close to that, so batteries recharge faster.

3. 120-Volt or 120/240-Volt?
Depending on where you boat, the AC shore power could be rated for either. It’s best to go with a charger that accepts both.

4. Durability
Epoxy-filled construction not only ensures true waterproofing, but it also eliminates potential shock damage, prevents condensation inside the charger and eliminates potential sparking.

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Safety
In addition to complying with the ABYC’s safety standard, does the charger have other safety features? Powermania’s Turbo M220V2 has backup thermal sensors and a waterproof cooling fan.

Quick Tip: As per ABYC standard 31.5.5.7, never install a battery charger above batteries. The corrosive gases created during charging can ruin the charger or ignite and cause a fire.

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