Marine help with product choice

Been thinking about this a lot lately because I'm doing something vaguely similar with the shepherd's hut — trying to figure out which battery chemistry plays nicely with a single charging source that wasn't really designed with lithium in mind.

Saw a thread elsewhere where a marine mechanic was scratching his head over a 54A alternator feeding two battery banks, and honestly it got me wondering how many of us are bodging together setups where the charging source is the weakest link rather than the batteries themselves.

My current headache: Victron's MPPT controllers are absolute legends and handle the lithium/AGM question brilliantly on the solar side, but the moment an alternator enters the chat it gets messy fast. A stock marine or vehicle alternator will happily cook itself trying to charge a hungry LiFePO4 bank that just sits there demanding more, more, more at full current.

Anyone here running lithium off a single smallish alternator — marine or otherwise — without fitting a dedicated DC-DC charger like the Victron Orion or similar? Because the conventional wisdom seems to be "don't even think about it without one," but I suspect half the boats on the Solent are doing exactly that and getting away with it.

Also curious whether people are going Fogstar Drift cells for marine/off-grid hybrid builds or sticking with something more traditional. The Drift's discharge rate seems fine for my EV charging experiments but I've no idea how it'd cope bobbing about on salt water.

Weigh in if you've got alternator-meets-lithium experience — genuinely trying to work out if I'm overthinking this or if the alternator really is the thing that'll bite me.

@SamFrost the single-source charging scenario is where chemistry choice really matters. On my narrowboat I run LiFePO4 (Fogstar Drift cells) precisely because the BMS handles the tighter voltage window gracefully when you've only got, say, shore power or a single alternator feeding it.

With one charging source you lose the redundancy that masks poor BMS behaviour — so avoid cheap unbranded BMSs regardless of chemistry.

Key consideration for a shepherd's hut: are you weight-constrained? LiFePO4 is heavier than NMC but the thermal stability is far superior for an unattended structure. A Victron SmartShunt paired with whatever chemistry you choose will at least give you accurate SoC monitoring when you can't babysit the system.

What's your single source — solar, hook-up, or vehicle alternator? That changes the charge profile requirements significantly.

@SamFrost and @PN_Camper — ooh this is relevant to me too! I'm currently wrestling with exactly this on my narrowboat. Quick question though — when you say single charging source, do you mean genuinely only solar, or does an alternator count as a second source? I ask because my setup is solar primary but I do run the engine occasionally and I've been trying to figure out whether that complicates the BMS requirements.

Also has anyone had experience with Fogstar Drift cells in a marine environment specifically? Wondering about the humidity side of things — a narrowboat is a very different beast to a static garden office install in terms of moisture and vibration.

@SamFrost @LindaClark90 funny you should both land here at the same time — I went through exactly this rabbit hole before settling my narrowboat setup.

The bit nobody warns you about is how the single source charges, not just that it charges. My solar-only winters were brutal on a previous lithium setup because the BMS kept throwing a fit during low-light partial cycles. Chemistry tolerance of that pattern varies massively.

Worth asking: what's the actual source? Engine alternator, solar, shore power? Each one has a different conversation attached to it. My Victron kit handles the profiling, but the battery still needs to be matched to the expected charge behaviour, not just the voltage numbers on the spec sheet.

What's the shepherd's hut running — a panel, a genny, or something more creative?

@SamFrost @LindaClark90 worth flagging that with a single charging source, your charge profile consistency becomes critical — LiFePO4 is far more forgiving here than AGM because the absorption phase is much shorter and less fussy.

On my static van I've got a Victron SmartSolar feeding Fogstar Drift cells, and the Bluetooth integration means I can actually see what the battery is doing throughout the charge cycle — invaluable for diagnosing whether your single source is actually getting the job done.

For a shepherd's hut or narrowboat specifically, I'd also think carefully about cycle depth — if you're drawing heavily each evening and relying on one source to recover, LiFePO4's genuine 80-100% usable capacity versus AGM's realistic 50% changes the whole system sizing calculation considerably.

What's the single source — solar, alternator, or shore power? That changes the answer meaningfully.

Boat angle here — did exactly this faff on my narrowboat two years ago. Ended up with Fogstar Drift LiFePO4 cells and honestly the single-charger situation is fine as long as your BMS is doing its job properly. The flat discharge curve that catches people out is actually your friend here — you get usable capacity right until the BMS kicks in, rather than watching voltage sag all afternoon wondering if you've got 40% left or 4%.

@LindaClark90 the narrowboat context matters because you're probably looking at a DC alternator as your single source? That's where things get spicy — make sure whatever charger/DC-DC converter you're running between the engine and the lithiums is actually lithium-aware. Sterling and Victron both do decent units for that.