Battery Bank Cost by Chemistry
Two owners on the same dock can spend $400 or $4,000 building a house bank of the exact same size, and the only real difference is the chemistry they picked. I watched that happen last spring on two nearly identical 30-foot trawlers moored three slips apart, both wanting around 300 amp-hours of usable power. One went flooded lead-acid and paid for it later. The other went lithium and winced at the register but hasn’t touched the bank since.
Chemistry is the single biggest lever on what a battery bank costs, both the day you buy it and every year you own it. A “house bank” is just the batteries that run your lights, fridge, electronics, and inverter, separate from the battery that cranks your engine.
Here’s where the money really goes, chemistry by chemistry.
The four chemistries and what they cost
Four options cover almost every boat: flooded lead-acid, AGM, gel, and lithium iron phosphate (LiFePO4, a safer, longer-lasting lithium type). Each buys you a different mix of price, weight, lifespan, and how much of the rated capacity you can actually use.
Flooded lead-acid is the old workhorse. You can buy a Group 31 deep-cycle flooded battery (roughly 100 to 105 amp-hours) for $130 to $200. The catch is you should only pull it down about halfway before you shorten its life, so a 100Ah flooded battery really gives you about 50 usable amp-hours.
AGM (absorbed glass mat, a sealed, spill-proof lead-acid battery) runs $220 to $350 for a similar Group 31. It tolerates deeper discharge, charges faster, and needs no watering. Gel batteries sit close to AGM on price, often $250 to $400, but they are fussy about charge voltage and have mostly been squeezed out by AGM. If you want the full comparison of these three, our guide on AGM vs Flooded vs Gel Batteries lays out the trade-offs in detail.
Lithium is the expensive line on the shelf. A quality 100Ah LiFePO4 marine battery runs $250 at the budget end to $900 at the premium end, with most sensible buyers landing around $400 to $600.
Why usable capacity changes the whole math
This is the mistake I see most weekends: an owner compares the shelf price of a flooded battery against a lithium one and declares lithium a rip-off. They’re comparing the wrong number.
What you care about is usable amp-hours, the energy you can actually take out without wrecking the battery. Flooded lead-acid hates deep discharge, so you plan around 50 percent depth of discharge. AGM handles roughly 50 to 60 percent comfortably. Lithium happily gives you 80 to 100 percent, cycle after cycle.
So to get 200 usable amp-hours, you need about 400Ah of flooded batteries but only 200 to 220Ah of lithium. That single fact narrows the price gap far more than people expect. Our explainer on depth of discharge covers why pulling a lead battery too low ages it so fast.
Cost by chemistry: a real comparison table
Here’s how a 200-usable-amp-hour house bank prices out across chemistries in 2026, including the extra batteries lead-acid needs to hit the same usable number. Prices are for the batteries only; wiring and labor come next.
| Chemistry | Rated Ah needed | Battery count (Group 31) | Battery cost only | Rough usable life | Cost per usable Ah-year |
|---|---|---|---|---|---|
| Flooded lead-acid | ~400 Ah | 4 | $520 – $800 | 3 – 5 years | $0.65 – $1.30 |
| AGM | ~360 Ah | 4 | $880 – $1,400 | 4 – 7 years | $0.65 – $1.75 |
| Gel | ~360 Ah | 4 | $1,000 – $1,600 | 4 – 6 years | $0.85 – $2.00 |
| Lithium (LiFePO4) | ~220 Ah | 2 – 3 | $700 – $1,800 | 8 – 15 years | $0.25 – $1.10 |
Read the last column twice. That’s cost per usable amp-hour per year of service, and it’s where lithium quietly wins even though its shelf price is the highest. The cheap flooded bank costs the most attention and the most replacements.
The costs the shelf tag never shows
The batteries are the headline, not the whole bill. On most installs I’ve done, the batteries are only 40 to 70 percent of the total project cost.
Every chemistry needs marine-grade tinned cable (tinned copper resists corrosion better than bare copper), lugs, and proper fusing. For a 200Ah-plus bank feeding an inverter, you’re running heavy 4/0 or 2/0 cable, and that copper is $8 to $15 a foot. Add a main fuse, a busbar or two, and heat-shrink lugs, and wiring alone lands at $150 to $500.
Then there’s charging. Lead-acid is forgiving and works with almost any charger. Lithium needs a lithium-profile charger and usually a DC-DC charger ($150 to $400) so your engine’s alternator charges the bank safely. That’s a real cost, and it’s part of why a lithium project runs higher than the battery price suggests.
Labor, and the total-of-ownership picture
If a yard does the work, budget 6 to 12 hours at $100 to $175 an hour for a mid-size bank. That’s $600 to $2,100 in labor on top of parts, and it’s roughly the same regardless of chemistry, since the wiring work is similar. A DIY owner who can crimp a lug and read a wiring diagram saves most of that.
Now stretch the timeline to ten years. A flooded bank that costs $650 today may need replacing two or three times, so you’re buying it two or three times, plus the labor to swap it each time. A $1,400 lithium bank you install once often outlives the boat’s next owner.
That’s the real accounting. A cheap bank that dies in three years and a bank that runs fifteen are not the same purchase, even when the first receipt is smaller. Cheap batteries fail in predictable ways, and our piece on why cheap boat batteries fail shows the pattern.
Where solar changes the equation
If you’re adding solar, chemistry matters even more. Lithium accepts charge fast and takes it right up to full, so it captures more of a sunny afternoon than lead-acid can. A pairing that pays back faster is covered in our Marine Solar Power Setup Guide, and the BoatUS library has good background on matching charging to house loads.
Which chemistry actually fits your wallet
If you use the boat 20 to 30 nights a year, run modest loads, and don’t want a big upfront hit, flooded or AGM is honest money. A flooded bank around $500 to $800 in batteries will serve a weekend cruiser fine for years, as long as you keep it charged and don’t run it flat.
If you liveaboard, cruise long, run a fridge and inverter hard, or you’re tired of replacing lead every few seasons, lithium earns its price. The upfront number stings, but the cost per usable amp-hour over a decade usually beats everything else, and the weight savings are a bonus on a smaller boat.
Whatever you pick, size and wire it right before you fret over the receipt. Start with the Marine Battery Bank Setup Guide to see how the pieces fit together, and if you’re combining batteries to reach your target voltage or capacity, our walkthrough on wiring batteries in series and parallel keeps you from making an expensive wiring mistake on top of an expensive bank.
Frequently asked questions
Which battery chemistry is cheapest for a boat house bank?
Flooded lead-acid is cheapest to buy, at roughly $130 to $200 per Group 31 battery. AGM sits in the middle around $220 to $350, gel is slightly higher, and lithium is the priciest per battery. But flooded gives you only about half its rated capacity, so the cheapest sticker is not always the cheapest bank over time.
How much does a 200 usable amp-hour bank cost by chemistry?
In batteries alone, plan roughly $520 to $800 for flooded, $880 to $1,400 for AGM, $1,000 to $1,600 for gel, and $700 to $1,800 for lithium. Lead-acid needs more rated capacity to hit the same usable number. Wiring, fusing, charging gear, and labor then add several hundred to a couple thousand dollars on top.
Why is lithium worth more even though it costs the most up front?
Lithium gives you 80 to 100 percent of its rated capacity versus about 50 percent for flooded, so you buy fewer batteries for the same usable power. It also lasts 8 to 15 years instead of 3 to 5, so you replace it far less often. Over a decade the cost per usable amp-hour usually comes out lowest.
What extra costs come with a battery bank besides the batteries?
Every bank needs marine-tinned cable, lugs, busbars, and proper fusing, often $150 to $500. Lithium also needs a lithium-profile charger and usually a DC-DC charger. If a yard does the install, add 6 to 12 hours of labor. Batteries are often only 40 to 70 percent of the total project cost.
Is a cheap flooded bank a false economy?
It depends on how you use the boat. For 20 to 30 nights a year with modest loads, a well-maintained flooded bank is honest money and can last years. For hard daily use or a liveaboard, a flooded bank you replace two or three times in a decade often costs more than one lithium bank you install once.
