Narrowboat lithium conversion - was it actually worth it after 18 months?

Finally got enough data to give an honest verdict on swapping out the old AGM bank on my 57ft trad stern.

Ditched 400Ah of AGMs for 200Ah of Fogstar Drift LiFePO4 last spring. Sounds mad going smaller, but usable capacity is actually better — I'm pulling from a genuine 80-90% DoD rather than the 50% AGM limit. Victron MultiPlus-II doing the inverting/charging, Cerbo GX keeping an eye on everything. Resting voltage behaviour still catches me out occasionally but nothing serious.

Biggest wins: the weight saving is noticeable on trim (AGMs were all port side, boat sat slightly skewed), charging from the Beta engine alternator is faster with a Victron Orion-Tr Smart DC-DC in the loop, and I'm not stressing about leaving the boat all winter at partial charge. Biggest surprise headache: the BSS examiner had never seen a LiFePO4 setup before and got a bit twitchy. Had to walk him through the BMS protection settings on-site.

So — anyone else done a similar swap on a live-aboard or continuous cruiser? Curious whether people are finding 200Ah genuinely sufficient for year-round use or if I'm going to regret not going bigger once the dark months really bite.

CamperBaz replied:

@ExBrickie Great thread, really interested to hear the full verdict! The usable capacity maths always catches people out at first glance - your 200Ah LiFePO4 at ~95% usable is genuinely more practical than 400Ah AGM where you're nervously stopping at 50% discharge to protect the batteries.

I did something similar on my campervan and the flat discharge curve alone was worth it - no more watching 12v appliances struggle when the AGMs got down to 70%.

Couple of questions if you don't mind:

• How's the Fogstar BMS handled the cold nights? I had a few sub-zero mornings last winter where I was glad I'd sorted low-temp cutoff
• Any issues with your alternator charging setup? That's where narrowboats can get complicated compared to vans

Looking forward to the full breakdown! 🛶

My shepherd's hut runs Fogstar too and honestly 200Ah lithium makes 400Ah AGM look like a damp squib — the usable capacity maths hits different when your batteries actually deliver what's on the tin rather than sulking below 50%.