Swapped to lithium on my 28ft Moody – shore power charger still playing up

Made the exact same leap on my tiny house setup last year — lead-acid to lithium — and the charger compatibility headache is real. It's not just a boat thing.

The core issue is that most older shore power chargers are still chasing that absorption/float curve designed for lead-acid. Lithium wants a proper CC/CV profile and, crucially, it needs to stop when it's done rather than sitting there trickling away. That trickle that kept your old AGMs happy will slowly stress a lithium BMS over time.

A few things worth checking:

• Does your charger have a lithium mode? Some units have it buried in the settings. Victron's Blue Smart range does it brilliantly, and I've seen a lot of boaters swear by them for shore power.
• What's your BMS doing when the fault shows up? If it's cutting out under charge, your charger voltage might be pushing past the pack's ceiling.
• Is it a 12V or 24V system? Worth confirming your charger matches, because some converters behave oddly when you change battery chemistry without updating the voltage setpoints.

My honest recommendation after going through the faff myself — just replace the charger. A Victron IP22 or IP65 (depending on your install space) will talk properly to lithium and you'll stop chasing ghosts. Fogstar cells and a Victron charger is a combination I've seen work reliably time and again.

What charger are you running currently? That'd help narrow it down. Others on here will have boat-specific experience I lack — would be good to hear from anyone who's dealt with shore power on a Moody specifically.

VoltJack | 847 posts

@Chippy - spot on about charger compatibility being universal, not just marine. The bit that catches most people out with lithium on boats specifically is the absorption/float stage behaviour. Many older shore power units just won't let go of that float voltage, and some LiFePO4 BMS boards absolutely hate sitting at 13.6v indefinitely - either throwing fault codes or disconnecting entirely.

Worth checking whether your charger has a dedicated lithium profile or if you're bodging it onto an AGM setting. Some Victron units let you customise absorption cutoff current which is a decent workaround if a full replacement isn't in the budget right now.

What charger are you running currently? That'd narrow things down considerably.

Really relevant thread for me — I've got a Victron IP22 on my 28ft narrowboat and went through exactly this pain when I swapped to Fogstar lithium cells last spring.

The bit that caught me out was the absorption voltage — my old charger was pushing 14.7v which my BMS absolutely hated. Had to dig into the Victron app and create a custom Li profile capping absorption at 14.2v and dropping float to 13.5v.

Quick question for @Chippy — was your shore power charger a single-bank or multi-bank unit? I'm wondering whether the multi-bank versions handle the transition to lithium profiles any differently, because I've got a second bank for my bow thruster and getting both to play nicely simultaneously was a proper faff.

Anyone else running a Mastervolt unit had similar issues? Seeing them quite a bit on the marina pontoon lately.

BordersExplorer | 1,203 posts

Worth flagging the absorption voltage ceiling specifically — most older shore power chargers top out at 14.4V absorption and won't let you reprogram it, which leaves lithium perpetually under-charged. You essentially lose 10-15% of your usable capacity without realising it.

On my shepherds hut build I solved this by fitting a Victron IP65 between shore power and the battery, bypassing the boat's original charger entirely rather than wrestling with it. Cleaner solution than trying to hack legacy firmware.

@CornishBoater — curious whether your IP22 is the single or three-output version? The three-output model has separate profile programming per output, which occasionally gives you a workaround if one bank is configured differently.

Also worth checking whether the BMS on your new lithium bank has a high-voltage cutoff that's triggering disconnects — that can look like a charger fault when it isn't.

Been through this exact scenario on my narrowboat. One thing nobody's mentioned yet — check whether your BMS has a charge enable signal you can wire to the charger's remote on/off. Victron units (IP22, Blue Smart etc.) support this natively, and it means the BMS can simply cut the charger rather than relying on voltage cutoffs.

Also worth checking if your charger has a lithium preset buried in the settings — several older units do but it's not obvious from the front panel. My previous Mastervolt needed a laptop and the MasterAdjust software to unlock it.

If neither option works, a Victron Battery Protect inline is a reasonable stopgap while you budget for a proper lithium-compatible unit.

@Chippy my shepherd's hut Fogstar lithium setup gave me the same grief until I realised my old charger was basically trying to "top up" the batteries like they were still full of lead acid guilt 🐑🔋

The equalization mode is the sneaky killer — if your charger randomly fires that off, your BMS will throw a proper tantrum and disconnect everything at the worst moment.

Worth checking if your charger has a dedicated lithium profile you can select, or failing that, manually locking it to a fixed absorption voltage around 14.2V and calling it done — Victron kit usually lets you do this cleanly via VictronConnect without needing a degree in misery.