Powering Your Boat: The Ultimate Guide to Energy Storage & Usage
Want to keep your boat powered efficiently without running out of juice? Whether you're a weekend cruiser or a full-time liveaboard, managing energy storage is key to a smooth sailing experience.
In our first article, Electrical Energy – Powering Your Boat Efficiently , we talked about how energy is generated on a boat. Now, let’s dive into the next big question: How do you store and use that energy efficiently?
Battery Banks: The Heart of Your Boat’s Power
The most common way to store energy on a boat is in your battery bank. Majority of boats have a 12V battery bank but you may have 24V or even less common a 48V battery bank. A battery bank is composed of multiple cells or multiple batteries, but when it is wired together we typically refer to it as the "house battery" or "house bank". This is separate from a starter battery that cranks your auxiliary diesel engine.
Battery banks are measured in Amp-Hours (Ah) or Kilowatt-Hours (kWh), and today’s boaters have more choices than ever when it comes to battery types:
- Lead Acid (LA), Sealed Lead Acid (SLA), Gel, and Absorbed Glass Mat (AGM): Traditional, widely available, but heavier and lower in efficiency.
- Lithium (Li-Ion) – Specifically Lithium Iron Phosphate (LiFePO4 / LFP): The best option for boats due to safety, longevity, and lightweight properties. (Not all lithium batteries are safe for marine use, so stick with LFP!)
Larger boats typically have bigger battery banks, and with good reason - they have more energy demands and have the space to store them. A typical 35-50 foot boat will have around 200-400 Ah (2.4 - 4.8 kWh) of usable battery capacity. But if you're running a high tech, power hungry setup, you might go much bigger - like we did. Our 40 ft boat, Cosmos, runs on a 1320 Ah (16.6 kWh) Victron Lithium Batteries, with 80-90% usability, meaning we can tap into 1056 Ah (13.3 kWh) of stored power without compromising battery life.
Beyond Batteries: Other Ways to Store Energy
Batteries aren’t the only way to store energy onboard. Here are two ways you’re already storing power:
- Water Heaters: A 6-gallon water heater holds over 1 kWh of stored energy - perfect for capturing excess solar power.
- Refrigeration & Freezing: Your fridge and freezer “store cold,” which helps maintain temperature longer before running the compressor.
If your energy source is "free", an example would be from excess solar, it would be wise to 'store' this somewhere. When we have surplus energy, we maximize storage by turning on our water heaters and setting our freezer to its coldest setting. We also store energy in our 18V cordless tool batteries, which together hold about 1 kWh - not a bad backup!
Energy Budget: Making Power Last
Think of your boat’s energy like a bank account - power goes in, power goes out, and the goal is to always have more than you spend. The challenge? Predicting both your power generation and usage accurately.
Here’s how we rank Cosmos’ biggest energy consumers from largest to smallest:
1. Refrigeration: 2 to 2.25 kWh/day
- (1 kWh/day) Custom-built 7 cubic foot fridge: Cabinet style with front opening doors which is convenient for ease of use but not the best for efficiency.
- (0.7 kWh/day) SnoMaster Expedition 85L Freezer: Double doors that are top loading. This is our primary freezer and we love how insulated this freezer is. It's also very spacious and I can tell you it holds a lot of bacon!
- (0.5 kWh/day)Engel 40 quart portable AC/DC: Swaps between fridge/freezer depending on needs. This is a great all around unit.
2. Starlink Mini: 0.6 kWh/day
We upgraded from the power hungry original to the most efficient Starlink Mini - which uses half the energy and while it is the lowest performing it still meets our needs.
3. Electric Cooking: 1-3 kWh/day
We balance using our induction cooktop with cooking on our Magma grill. Our grill is connected to a fiberglass tank that has propane. Cooking on the grill is not only a tasty way to cook (yum!), but a great way to save energy on cloudy days.
- 2 Burner Induction Cooktop Cooking on inductions does NOT heat up the interior of the boat like propane/gas or normal electric - so it's a much cooler way to cook. It's also the most efficient of the electric methods, using between 500-1500W.
- Electric Countertop Oven My wife bakes about once a week - we do love cakes and cookies! However, an oven can consume a lot of power due to a lack of insulation, using 1500W when heating.
- Instant Pot Duo 3 Quart This is the smallest Instant Pot which is the perfect size for our boat. It uses 700W while heating. It is very efficient due to being well insulated and has high pressure for quick cooking time.
- Rice Cooker A quick way to make rice, steam vegetables or boil some water for pasta. It uses a maximum 300W when heating.
- Bread Maker We love our bread maker to make our favorite banana bread recipe. Everyone says it's the best banana bread they have ever had! Message us for the recipe.
- KitchenAid Artisan Mini Stand Mixer 250W
- Ninja Blender 1000W
- Ninja Food Chopper 200W
- Ninja Slush Machine 200W. I'm not sure we can live without this now, but it uses about 1kWh. Everyone knows I'm a frozen drink addict!
- Electric Kettle 1500W when heating.
- Instant Pot Magic Milk Frother 600W when heating. Necessary for Su's morning tea!
4. Air Conditioning – The Holy Grail!
We use two Mabru 12V DC 12,000 BTU/Hr removal (550-600W each when on maximum). They’re twice as efficient as standard marine AC units, meaning we stay cool without breaking the power bank. The cool part - inverters aren't necessary! Air conditioning is normally a luxury, but necessary to use when there is high humidity or extremely hot days.
5. Compact Dishwasher: 0.6 kWh/day
A luxury, yes, but also a huge convenience.
6. Water Makers: 0.5 to 1 kWh/day
Water makers are used to turn seawater into potable water. There are two major types, "energy recovery" and "normal". Energy recovery models are energy efficient and worth the additional investment since they produce twice the water per kWh compared to standard models. This is important for us since we use water for drinking, cooking, showering and washing laundry. We installed Spectra Cape Horn Edition CHE.
7. Electronic Gadgets: 0.5 kWh/day
Laptops, tablets, and phones are surprisingly light on energy. We charge these devices directly from 12v sockets - avoiding the need to run inverters to make AC power. Your laptop runs on DC, your laptop battery stores DC, your solar makes DC so it is best to use DC and not use an AC power/Inverters since this would be very wasteful!
A good rule of thumb, the lighter the laptop, the less energy it consumes. Su is a MAC girl so she loves her Mac Air 13" and Chris is a Windows guy and loves his Lenovo X1 Carbon 12th Gen Touchscreen.
Final Thoughts: Efficiency is Everything
The secret to a well-powered boat? Choose efficient appliances, maximize storage, and turn things off when not in use. How much power you generate determines how much you can use, so plan accordingly. And if you’re in doubt - go solar, go lithium, and get efficient!
Got any cool power-saving tricks or gadgets you can’t live without? Drop us a message - we’d love to hear from you!
Read our other articles:
Chris & Su Wallace
Chris & Su Wallace
Chris & Su Wallace
Chris & Su Wallace
How to Save Big on Sailboat Parts: Our Top Buying Secrets and Where to Shop Online
Sailboat Parts Reviews: RuuviTag Pro Sensor
How to make Winch Covers with an inside choker using SCRAPS - FREE Pattern
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