Swapped to lithium on my narrowboat – shore power charger now playing up

Made this switch last year on my static setup rather than a boat, but the charger compatibility issue is identical — worth sharing.

The problem is almost certainly your charger still being set to a lead-acid profile. Most older shore power units will push a float voltage around 13.6–13.8V which is fine for AGM but lithium wants to sit at 13.2–13.4V at rest. Over time that constant slight overvoltage stresses the cells even if it doesn't immediately trigger your BMS.

A few questions that might help diagnose it:

• What charger are you running? Some older units have no lithium profile at all
• Is the BMS cutting out, or is it something else you're seeing?
• Which battery? Fogstar Drift cells behave differently to, say, a Victron Smart Lithium in terms of how aggressively the BMS responds

If your charger has no lithium mode, you've got a couple of options. Either replace it with something like a Victron Blue Smart IP22 which handles lithium properly, or fit a DC-DC converter between shore power and the bank — crude but it works.

The narrowboat community seems to have a lot of people running mismatched chargers on lithium conversions because the switch to LiFePO4 happened faster than the shore power infrastructure caught up with it.

What charger model are you on? Might be able to point you somewhere more specific.

@Taffy62 — yeah the absorption/float voltage mismatch is a classic gotcha when swapping chemistries. Most older shore power chargers are hardwired for lead-acid profiles and will either undercharge or, worse, push too high a float voltage into your lithium bank long-term.

Worth checking whether your charger has a user-selectable lithium profile first — some Victron Blue Smart units do. If not, a proper lithium-compatible charger is the cleaner fix rather than bodging the settings.

I went through exactly this on my tiny house build when I switched to Fogstar Drift cells. Ended up replacing my old Sterling charger with a Victron IP22 — night and day difference, BMS stops throwing tantrums now.

If budget's tight, the Renogy DC chargers aren't bad either, though I'd personally stick with Victron for anything mains-connected.

Ooh this brings back memories — I had exactly this chaos when I sorted out my static caravan setup a couple of years back. My old charger was stubbornly pushing 14.7V absorption like it was still babysitting lead-acid batteries, and my lovely new Fogstar cells were absolutely not happy about it.

What finally sorted me out was grabbing a Victron Blue Smart IP22 — it's got proper lithium profiles baked in and you can tweak everything through the app. Bit of an outlay but honestly it's been faultless since.

@Wardy is spot on about the voltage mismatch being the culprit. Worth also checking whether your charger has a configurable float voltage — lithium really wants around 13.5V float rather than the 13.8V that lead-acid chargers default to. That slow overcharging adds up over time.

Really relevant thread for me this — I've got a static caravan setup and I'm just about to make the jump from AGM to lithium (looking at Fogstar Drift cells). My concern is exactly this charger compatibility thing before I even start.

Quick question for anyone who's done it: is it worth just replacing the shore power charger at the same time as the batteries, rather than trying to fiddle with the existing unit's settings? Mine's an older Sterling unit — no idea if it's even got a lithium profile on it.

Or does Victron's Blue Smart range sort all this out automatically? I've seen a few people swearing by them but they're not exactly cheap. Is the peace of mind worth the premium, or am I overthinking it and the Sterling will be fine with a manual tweak?

@OldSparky — worth checking what charger you're currently running before you commit to the swap. Some older units genuinely can't be reprogrammed for lithium charge profiles, and you'll end up buying a replacement anyway.

I went through this myself — had a fairly decent AGM charger that I assumed would be fine with a firmware update, turned out there was no update available and the absorption voltage was fixed. Ended up going with a Victron Blue Smart, which lets you set the profile properly via the app.

One thing I'd specifically check: does your current charger have a dedicated lithium mode, or just an adjustable voltage ceiling? There's a meaningful difference between the two when it comes to how the charger handles the tail current phase.