LiFePO4 & power systems
Marine Lithium Battery Systems
Usable capacity, not rated capacity
A 400 amp hour lead-acid bank gives you roughly 150 usable amp hours. A 200 amp hour lithium bank gives you about 190. That is the whole argument. Most of the rest of this page is the consequences of it.
We are the largest EPOCH marine battery dealer in Washington, we hold stock, and we build the system around the bank.
LITHIUM
Decades of LiFePO4 experience.
We have been building lithium systems on boats for decades. Epoch batteries, the charging profile behind them, and the whole system around it.
Talk to us about your boat and we will tell you what it should have.
Rated capacity is not usable capacity
Every battery on the market is sold on a number. What matters is how much of that number you can actually take out of it, on your boat, in this water.
300Ah
Rated capacity, Epoch 12V 300Ah Group 8D.
3.84 kWh
Stored energy. Epoch hold reserve back, so what we measure in service runs at or above the rating.
6,000+
Cycles, with an 11-year manufacturer warranty behind it.
Capacity, weight and space
The same usable capacity, at 58 pounds instead of 486
Compare the labels and lithium looks like a modest saving. Compare what you can actually take out of the battery and it stops being close. Lead-acid is held to roughly 50% depth of discharge if it is going to last, so half of what is on the label was never yours to use.
A 255Ah Group 8D AGM — a good one, a Lifeline GPL-8DL — gives about 128Ah usable and weighs 162 lb. Two of them still only reach 256Ah usable. It takes three to match one Epoch 12V 300Ah, and three of them weigh 486 lb and fill three battery boxes.
The Epoch 12V 300Ah gives you 300Ah usable, weighs 58 lb, and drops into a Group 31 tray — 13.75 by 7.63 by 10 inches, against three 8D boxes at nearly 21 inches each.
That is 428 lb out of the boat and two battery boxes of locker back. On most vessels the bank sits aft and low, so it changes trim, draft and hole shot — the biggest weight change available without cutting the boat up.
CHARGING
The charging profile is the whole job
A lithium bank is only as good as what charges it. Get the profile wrong and you will never see the capacity you paid for.
Epoch specify it precisely:
Bulk and absorption 14.2–14.6V. Float 13.4–13.8V. Equalisation disabled. Temperature compensation disabled. Charge rate at 50% of bank capacity.
Most chargers on boats are not set up this way.
We set the alternator, the inverter-charger, the solar controller and the shore charger to match, then verify it under load. That is the part that decides whether the system works.
Starting
For starting, we fit a capacitor
KBi capacitive starting
From Kold-Ban International, sold for boats as BoatStartPlus. A KAPower supercapacitor is not a battery. It stores a burst, cranks the engine, and recharges in about thirty seconds from any 12V source. Charging and discharging do not wear it out.
It holds a charge for months, mounts in any orientation including upside down, and KBi rate it past a million cycles. Pair it with a deep-cycle house bank and starting stays independent of the bank — which is also how the house battery avoids a job its warranty excludes.
Or a dual purpose bank — Epoch 12V 300Ah
1,000A peak for 5 seconds, 800A for 10. Enough to crank and still hold 300Ah of house capacity, with 300A continuous in and out.
IP67, submersible to a metre. Internal heating charges down to −20°C. Victron CANBUS for closed-loop charging.
Or Epoch 12V 172Ah Group 31
1,000A peak for 5 seconds — roughly 1,000 CCA equivalent — with 200A continuous in and out and 172Ah of house capacity, in a Group 31 tray at 40 lb.
A cranking-capable BMS, rated for outboards to 250 hp where the engine and charging specs match. IP65, Bluetooth, 4,000+ cycles. No self-heating on this model, and not approved for series wiring — up to four in parallel.
The whole system
What a proper lithium install actually includes
A drop-in battery is not a drop-in system. Everything below is work that does not show up in a price comparison and decides whether you get ten years or two.
- Alternator protection. This is the one that burns alternators. Lithium will take everything an alternator can produce, indefinitely — and an alternator built to taper off against lead-acid will simply run flat out until it cooks itself. We fit external regulation with temperature sensing, or a DC-DC converter, so the alternator survives the upgrade.
- A BMS integrated with the charge sources, not just the battery. A cheap drop-in protects itself by disconnecting under load — which dumps the alternator and can take electronics with it. A proper system tells the charger to stop before anything opens.
- Class T fusing at the battery. Factory-trained, with proper circuit protection specified to the bank and installed to standard. Ordinary fusing may not interrupt that current, which makes it decoration.
- Low-temperature charge protection. Charging LiFePO4 below freezing permanently damages the cells. Northwest boats sit through winter, so this is not theoretical here.
- Cable and busbars sized for the current you will actually pull — not whatever was adequate for the lead bank.
- Shunt-based monitoring. State of charge has to be measured, not guessed from voltage — and lithium’s flat curve makes voltage guessing meaningless anyway.
- Every charge source set correctly — alternator, shore charger, solar, generator. One wrong profile undoes the rest.
Done properly, the bank reaches full every time and lasts the decade it was sold on.
Epoch 11-year warranty
Eleven years of cover, and the install that protects it
Epoch warrant their LiFePO4 batteries for up to eleven years. On most models that is free repair or replacement through year five, then a comparable-product remedy at a reduced price through year eleven. Epoch-branded chargers carry two years, accessories one. It is the longest cover in marine lithium — and the terms are worth understanding before the battery goes in, rather than after.
Register it inside ninety days
Epoch require registration within ninety days of purchase. Inside that window the clock runs from the day you bought the battery. Miss it and the warranty period is counted from the battery’s manufacturing date instead. Ask us at handover and we will walk you through it.
The install is what protects it
Read Epoch’s exclusions and most of them are wiring rather than chemistry — improper installation, loose or corroded terminals, undersized cable and poor crimps, series and parallel connections beyond what the model allows, and faults elsewhere in the vessel’s electrical system. We install to Epoch’s specification and to our own written procedure, and we document it.
Cranking is a model choice
Epoch do build cranking batteries — dual-purpose models with a cranking-capable BMS, where a standard deep-cycle lithium would fold under a starting load. Their warranty excludes repeated starting on models not built for it, so the whole thing turns on specifying the right one. Where a boat keeps a deep-cycle bank, we add a KBi capacitor rather than ask it to crank.
Coverage varies by model line. Full terms, the model-by-model remedy schedule, exclusions and the claim process are published by Epoch on their 11-year warranty page.
What you actually get
A bank you can use all of. Voltage that holds up. An hour of engine time that genuinely refills it. An alternator that survives the season. Monitoring that tells you the truth, and a system we can look at remotely when something is odd.
And a bank that is still doing that in ten years, because it was installed as a system. Talk to our marine electrical crew about what your boat actually draws — that is where the sizing conversation starts, not with a catalogue.
Free for every customer
A complimentary 18-point inspection
An expert technician tests the boat’s systems and writes up every point as Excellent, Good, Monitor, Attention or Critical — a written report telling you what is sound, what to keep an eye on, and what has to be dealt with before she goes back in the water. Free with every job.
EXCELLENT
GOOD
MONITOR
ATTENTION
CRITICAL
Essential Shipyard 