Anyone else running lithium on a narrowboat? Struggling to sort my charging sources properly

I've finally taken the plunge and swapped out the old AGM bank on my 57ft narrowboat for a 200Ah lithium (LiFePO4) setup from Fogstar. Brilliant so far in terms of usable capacity, but I'm now tearing my hair out trying to get all my charging sources playing nicely together. Running a 110A alternator off the Beta 43 engine, a 40A shore power charger (Victron Blue Smart), and two 175W solar panels on the roof going through an MPPT controller.

The main headache is the alternator side. I've got a Victron Cyrix-Li-Ct as my charge relay but I'm reading conflicting things about whether I need a proper DC-DC charger (B2B) in there to protect the alternator from the lithium just dragging it flat out. Some folks say the Cyrix is fine with a BMS that limits charge current, others are saying the alternator will cook itself within a season. My BMS cuts off at 100A charge current so in theory it's protected, but I'm not fully convinced.

Has anyone actually got a working setup on a boat with a similar engine alternator situation? Did you go down the B2B route (Victron Orion or similar) or are you running direct with a relay and just keeping an eye on it? Also wondering if the Beta 43 alternator is robust enough to handle sustained high loads — I've heard mixed things about Beta's stock alternators running hot.

Any real-world experience massively appreciated, especially if you're living aboard like me where reliability isn't optional.

@Dizzy83 running almost identical setup on my boat — Fogstar 200Ah with Victron kit managing the charging sources.

The key thing that sorted mine was a Victron Battery Protect on the load side and a proper DC-DC charger (I use the Victron Orion-Tr Smart 30A) between the alternator and the lithium bank. Don't just wire your alternator straight to LiFePO4 — you'll cook it when the BMS disconnects under a full charge. That isolated DC-DC unit saved my alternator.

For shore power I've got a Victron Blue Smart IP22 which talks nicely to the BMS.

A few things worth checking:

• Is your BMS communicating with your chargers?
• What's your alternator rating?
• Solar in the mix as well?

Once everything's talking properly it genuinely becomes a hands-off system.

JimButler | 847 posts

@Dizzy83 welcome to the lithium club! One thing that catches a lot of narrowboaters out is the alternator situation — your standard engine alternator absolutely needs a DC-DC charger (like a Victron Orion-Tr Smart) between it and the lithium bank. Running an alternator directly into LiFePO4 can fry it when the BMS disconnects under full charge, as there's nowhere for that energy to go.

@SimonThompson will likely back me up on this. What alternator are you running on your engine? Also worth checking whether your shoreline hookup at marinas is going through a proper lithium-compatible charger — some of the older onboard chargers don't like the flat charge profile lithium needs. What other charging sources are you working with — solar panels, shore power, just the engine?

Victron_Master | 2,341 posts

@Dizzy83 great choice going with Fogstar, solid cells. One thing worth sorting early on is your alternator situation — lithium's low internal resistance means it'll happily pull your alternator hard and cook it, especially on longer cruises. A proper DC-DC charger like the Victron Orion-Tr Smart between the alternator and your lithium bank is the sensible way forward rather than direct connection. It'll protect the alternator and give you proper charge profiling.

Also, what are you using to tie all your charging sources together? If you've got solar and a shoreline as well, a Cerbo GX coordinating everything makes a massive difference — prevents your sources fighting each other and gives you proper state-of-charge visibility. Happy to walk you through the wiring logic if needed.