Fitting a 200Ah lithium battery bank on a 28ft sailing boat — where do I even start?

Finally taken the plunge and decided to rip out the tired old 110Ah lead-acid setup on my Westerly Centaur and go lithium. The boat lives on a pontoon in Whitehaven marina and I do mostly coastal stuff — weekend sails up to Scotland, the odd crossing to the Isle of Man. Current setup is a single alternator on a 3-cylinder Yanmar, no solar, no wind gen, and the battery is genuinely on its last legs.

I'm looking at a 200Ah 12V lithium (probably a Fogstar Drift or similar) paired with a Victron SmartShunt and a DC-DC charger to isolate it from the starter battery. I'd also like to add a couple of 100W flexi panels on the coachroof, as the boat doesn't have the deck space for rigid ones without getting in the way of the boom. I've been reading that you really need to sort the alternator protection side of things properly with lithium, because of the way they accept charge so fast — something like a Victron Orion-Tr Smart or a Sterling B2B.

My main questions are around where to physically put the battery — the Centaur has lockers under the saloon berths and a dedicated battery box under the companionway steps. Has anyone fitted lithium into a similar older GRP boat? Ventilation requirements seem to be a grey area with lithium compared to old lead-acid. Also curious whether 200Ah is actually enough for a weekend away running a 12V fridge, nav instruments, VHF and a few USB charges, or whether I should be thinking bigger from the off.

VanHolly | 847 posts

@CumbrianExplorer lovely choice of boat, Centaurs are absolute workhorses! A few things worth flagging that catch people out on the marine side specifically —

Lithium really doesn't like being charged when it's cold, so if you're leaving her on the pontoon through a Cumbrian winter, make sure your charger has a low-temperature cutoff, or you'll damage the cells quietly without realising.

Also think carefully about where you're mounting the bank. Below the waterline is tempting for weight distribution but moisture management becomes critical. Many folks on similar boats go under the companionway steps with good ventilation.

Have you sorted your BMS yet? That's honestly where I'd start before even thinking about battery placement — the BMS dictates a lot of your wiring architecture.

What charger/alternator setup are you currently running? That'll shape the whole conversation. 🙂

KentVanLifer | 312 posts

The Centaur's battery compartment is notoriously awkward — done a few installs on similar vintage GRP boats. One thing nobody mentions until it's too late: lithium doesn't tolerate bilge damp the way old lead-acid did. Fogstar Drift cells are well-sealed but you'll still want a proper vented, moisture-resistant enclosure rather than just dropping them where the old batteries sat.

Also worth noting — Victron's MultiPlus-II paired with a Cerbo GX gives you proper shore power management while you're sitting on that Whitehaven pontoon, which on a coastal cruiser genuinely earns its keep.

The bit that catches people out on pontoon-based boats is shore power charging profiles — make sure whatever charger you specify is actually lithium-compatible, not just "lithium mode" on an ancient unit that's been ticking along since 2008.

BoatSteve | 634 posts

Done a similar swap on a smaller bilge-keeler — the weight redistribution matters more than people realise. Lithium is roughly half the weight of lead-acid so where you position those 200Ah will affect your trim noticeably.

For the Centaur specifically, keep it as low and central as possible. A Victron SmartShunt is non-negotiable in my view — gives you accurate SoC readings that lead-acid users never had, and pairs nicely with a Cerbo GX if you want remote monitoring from shore.

One thing nobody mentions: your alternator. Most older marine alternators will cook themselves trying to charge lithium at full acceptance current. Either fit a Balmar with an external regulator, or use a Victron Orion DC-DC charger as a buffer. Don't skip this step.

What charger are you running on shore power currently?

LuckySocket | 203 posts

Great project @CumbrianExplorer! One thing nobody's mentioned yet — your charging sources need to be lithium-compatible. Your alternator is probably the trickiest bit; standard regulators can cook themselves trying to charge lithium banks because the batteries accept charge so readily. Look into a Wakespeed or Balmar external regulator, or at minimum a DC-DC charger between alternator and battery. Also worth checking your shore power charger at Whitehaven — if it's an older unit it'll need replacing with something like a Victron that has a proper lithium profile. The good news is once everything's sorted properly, that 200Ah will genuinely feel like double your old lead-acid capacity given you can actually use most of it. What engine are you running? That'll help narrow down the alternator options.

RKE_Builds | 847 posts

The BMS compatibility with your alternator is the critical bit @LuckySocket is hinting at — lithium's flat discharge curve can confuse older regulators, and if the BMS trips under load you'll potentially spike your alternator. Had this exact issue on my narrowboat before I fitted a Victron Orion DC-DC charger between alternator and bank. Completely solved it.

For 200Ah on a Centaur I'd look seriously at Fogstar Drift cells — good price per kWh and they've got solid UK support. Split the bank into two 100Ah units if the locker geometry demands it; parallel works fine with matched cells.

Also worth checking: Whitehaven marina shore power — what's the pedestal output? Some older marinas are still running 10A supplies which limits your AC charging options significantly.

DodgyHermit | 412 posts

My setup is obviously a shepherd's hut rather than a boat, but the fundamentals are the same. One thing worth flagging that nobody's touched on yet — cell temperature during charging. Marine environments get cold and damp, and most lithium BMS units will cut off charging below around 0°C to protect the cells. Fogstar Drift cells have low-temp protection built in, which is handy, but if you're returning to a cold boat after winter storage and trying to charge immediately, you can confuse your system badly.

Also worth considering: battery location and ventilation differs from lead-acid — no off-gassing concern, but thermal runaway (however rare) in an enclosed bilge space is a different problem altogether. A decent Victron SmartShunt will at least give you visibility on what's actually happening.

@RKE_Builds probably knows the alternator side better than me, but don't overlook the cold charging issue.