The fastest way to charge boat batteries with a portable generator is to connect it to your shore power cord — not the built-in 12V outlet. After 17 years of living aboard and more cloudy winters than I care to count, this is the method that actually works.
Most cruising boats use a Honda EU2200i (Amazon) or its predecessor, the Honda EU2000i. The Hondas are quiet, reliable, and easy to find parts and service for worldwide. The main downside is price. A few copycat brands have been gaining traction among cruisers, with some reporting good results — though it’s still too early to know how they hold up long-term.
These small portables are not the same as built-in marine generators. Built-ins produce more power and are designed for marine conditions from the ground up. But plenty of cruising boats run small portables, and we did too.
Choosing a Portable Generator
If you start shopping, you’ll find many generators with more power for less money than the Honda. The key differences come down to noise and size. Avoid what’s called a construction generator — the noise is genuinely obnoxious, and you will not make friends in the anchorage. The Honda EU2200i is the quietest I know of. We ran both the EU2000i and the EU2200i, and the 2200 was noticeably quieter.
These generators weigh about 40 pounds and can run a battery charger, a watermaker, or power tools.
How to Connect the Generator to Charge Your Batteries
The Honda EU2200i and most similar generators come with a 12V outlet. Boaters often ask whether that’s the best way to charge. It isn’t. That outlet puts out only 8.3 amps — it will take all day.
Instead, use the generator’s 110V outlet (the standard household-style outlet) and connect it to your boat’s shore power cord. Your onboard shore power charger does the work, and you’ll get roughly 80 to 90% of whatever your charger is rated for.
Your shore power cord almost certainly needs an adapter to connect to the generator’s 15-amp outlet. If your boat has a 30-amp or 50-amp shore power cord, you need a 15-amp male to 30/50-amp female adapter (Amazon). Because we also used our generator to run the watermaker, we always kept a spare adapter aboard — dropping one overboard is a real possibility.
How Fast Will It Charge?
Charging speed is governed by two things:
- Your shore power charger’s rating. The generator isn’t usually the bottleneck — your charger is. A 30- or 40-amp charger limits your input to 30 or 40 amps, minus some system losses. We ran a 120-amp charger and typically saw about 75 amps going into the batteries. That’s a significant difference in how long the generator needs to run.
- How full your batteries already are. Lead-acid and AGM batteries accept charge more slowly as they approach full. The closer they are to topped-off, the less they’ll take in.
If you have solar panels, the smart move is to run the generator early in the morning when the batteries are at their lowest. Let the generator handle the bulk charge, then let solar finish the job. You can monitor your battery state of charge to see exactly when to shut the generator down.
If you’re not sure whether your charging system is sized right for your power needs, calculating your boat’s power requirements is worth doing before you invest in a larger charger.
Generator Safety Aboard
A portable generator on a boat requires care. Keep these in mind:
- Carbon monoxide is a serious risk. Make sure the exhaust is directed away from any cabin openings. Never assume the wind will take care of it.
- Install a CO alarm (Amazon) if you don’t already have one. This is non-negotiable.
- Don’t run the generator in the rain or leave it uncovered. Rain and electronics don’t mix.
- Carry enough fuel. Gasoline adds to your provisioning list, especially on longer passages.
A Note on Dual-Fuel Generators
Most cruisers already carry gasoline for the dinghy engine. But if your boat runs on propane for cooking and you have an electric dinghy motor, a dual-fuel generator that runs on either gasoline or propane is worth considering.
Two readers, Cabot and Dave, both use the Champion Dual Fuel Generator (Amazon). Cabot notes that propane burns cleaner but is less energy-dense than gasoline — about 1,800 watts instead of 2,000. He found the tradeoff worthwhile since he didn’t need to carry gasoline for anything else. He also points out that propane doesn’t go bad, it keeps the carburetor clean, and a 20-pound canister will run the generator continuously for about 24 hours.
There are also conversion kits for the Honda (Amazon), though they aren’t inexpensive.
I don’t have firsthand experience with the Champion, but the propane option makes real sense for boats already set up for it.
Why We Used a Generator
We lived primarily on solar power. But during winter months and stretches of overcast weather, solar alone wasn’t enough — and we’d run out of room to add more panels. Running the diesel engine just to charge batteries isn’t ideal either; diesels are happiest under a real load, not idling away for battery charging. A small, fuel-efficient portable generator was the right answer for us.
Ready to Learn More About Life Aboard?
Charging your batteries is one of the everyday skills that comes with living on a boat. If you want a clear, practical overview of what liveaboard life actually involves — boat systems, anchoring, provisioning, handling unexpected situations, and more — my course The Basics of Living on a Boat covers 31 topics that most people don’t realize they need to know until they’re already out there.
Carolyn Shearlock has lived aboard full-time for 17 years, splitting her time between a Tayana 37 monohull and a Gemini 105 catamaran. She’s cruised over 14,000 miles, from Pacific Mexico and Central America to Florida and the Bahamas, gaining firsthand experience with the joys and challenges of life on the water.
Through The Boat Galley, Carolyn has helped thousands of people explore, prepare for, and enjoy life afloat. She shares her expertise as an instructor at Cruisers University, in leading boating publications, and through her bestselling book, The Boat Galley Cookbook. She is passionate about helping others embark on their liveaboard journey—making life on the water simpler, safer, and more enjoyable.
Dave Brown says
Hello Cabot- I also have a Champion Dual Fuel 2000 W generator. I connected mine using a 30 amp to 15 amp adaptor to the shorepower cord through the 120V plug on the generator. I also used only propane to keep gasoline out of my lazarette. The generator, however, kept tripping its overload breaker. Have you experienced any similar issues?
Dave
Carolyn Shearlock says
I’ve never heard of an electric shock drowning with 12V solar.