Switched to lithium on the boat this season — worth every penny or false economy?

Finally pulled the trigger and ripped out the old AGM bank on my 32ft sloop. Was running 2x 110Ah AGMs which were about 4 years old and frankly knackered — barely holding 60% capacity. Replaced with a single Fogstar Drift 200Ah 12V LiFePO4 and honestly the difference is night and day. Usable capacity has effectively tripled once you account for the 80-100% DoD vs the 50% I was babying the AGMs to.

Paired it with a Victron SmartSolar 100/20 and a Renogy 200W panel on the coach roof. The Bluetooth monitoring via the Victron app is brilliant for keeping an eye on things when I'm below decks. Only issue I've hit is the BMS cutting out once when I accidentally left the inverter running overnight with nothing connected — drew it down too low. Sorted now with a low-voltage cutoff relay but it gave me a heart attack at the time.

Mooring is at a marina in the Solent so I do get decent solar hours in summer, but the boat sits untouched for weeks sometimes. With the old AGMs I'd come back to flat batteries and a sulphated mess. Now the LiFePO4 just... sits there holding charge. Self-discharge is almost nothing.

Has anyone else made the switch mid-season rather than waiting for winter? Curious whether the install headaches are worse when you're also trying to actually sail the thing.

DuctTapeDave94 | 847 posts | ⚓ South Coast

@MarineMike nice one, curious what you went with in the end — you cut off mid-sentence there mate!

I made the same switch last year on my 28ft bilge keeler. Went with a 100Ah LiFePO4 and honestly the usable capacity difference is night and day compared to AGMs where you're tiptoeing around 50% discharge.

One thing worth flagging — make sure your alternator isn't cooking the BMS when motoring. I had to fit a decent alternator protection relay because lithium absorbs charge so aggressively it can overheat older alternators. Bit of a gotcha that catches people out.

Also worth checking your shore power charger is lithium-compatible if you haven't already. Some of the older units will just confuse the BMS completely.

What solar setup are you running alongside it?

RelayProject | 1,203 posts | ⚡ Welsh Borders

@MarineMike Solid move — four-year-old AGMs on a boat are rarely worth nursing along. The real win with lithium on a sloop isn't just the capacity, it's the flat discharge curve meaning your instruments and autopilot behave consistently right down to low SOC rather than getting sluggish as voltage drops. Makes a genuine difference on longer passages.

One thing worth checking if you haven't already — your alternator. Lithium's acceptance rate can hammer older alternators hard, especially if you're motoring in after a crossing and the BMS is screaming for bulk charge. A decent DC-DC charger between alternator and battery is worth considering if you haven't gone that route.

What BMS did you end up with? And are you running a separate starting battery still or gone all-in?