Swapped out the old Victron MPPT on my narrowboat – few questions about the new settings

Not a narrowboat setup here but I run a very similar Victron MPPT configuration on my tiny house, so some of this should translate directly.

The absorption/float voltage settings are the ones most people get wrong after a swap. What battery chemistry are you running? If you've moved to LiFePO4 (Fogstar Drift cells are popular right now), the defaults Victron ships with are almost certainly wrong out of the box — you'll want absorption around 14.2V and float closer to 13.5V rather than the AGM defaults.

A few things worth checking in VictronConnect:

• Adaptive absorption — useful for lead-acid but disable it for lithium
• BMS assistant — if you've got a BMS with a relay output, worth wiring into the MPPT's remote on/off so the BMS can shut down charging in an emergency
• Battery temperature sensor — canal environments can get surprisingly cold overnight, especially moored up in winter. The Victron SmartSense dongle is cheap insurance

One thing narrowboats have that my setup doesn't is the complication of running alongside a BMV or Cerbo GX on a VE.Direct network. If you've got multiple devices on the same network, make sure you've only got one device set as the charge master, otherwise you'll get conflicting absorption timers and the whole system behaves oddly.

What MPPT model did you go from and to? The SmartSolar range logs much better data than the older BlueSolar units, so you should finally be able to see exactly what's happening through the day.

Would be interested to hear what panel array you're working with — roof space on a narrowboat is always a constraint.

Hey @LDVConvert, good shout on the tiny house comparison – the principles are essentially the same regardless of whether you're floating or static!

One thing worth flagging that's slightly different for marine setups though: corrosion and temperature swings on the water can affect your battery terminals and connections more than you'd expect on a fixed install, which can skew your voltage readings at the controller. Worth double-checking your wire runs and connections are solid before you fine-tune those absorption/float figures, otherwise you might be chasing phantom voltage drop issues.

What battery chemistry are you running? That'll make a big difference to where you want those settings sitting. LiFePO4 is a whole different ballgame compared to AGM or lead acid in terms of where you set absorption cutoff.

Good point from @LDVConvert and @StuWhite94 — worth adding that with LiFePO4 (if that's what you're running) the absorption/float gap matters enormously. On my Victron SmartSolar 100/30 paired with Fogstar Drift cells, I've got absorption at 14.2V and float at 13.5V, which keeps the BMS happy without top-balancing stress on every cycle.

One thing specific to marine environments worth flagging: temperature compensation. Victron's default coefficient is designed around lead-acid — if you've switched chemistry, double-check that setting is either zeroed out or correctly configured, otherwise your controller is applying voltage corrections that actively work against you in cold UK winters on the water.

The Victron Connect app makes this straightforward — just don't blindly trust the preset profiles without cross-referencing your battery manufacturer's spec sheet.

@VanGill raises the LiFePO4 point, which is crucial — but I'd push back slightly on glossing over which LiFePO4. There's a meaningful difference between cells with an integrated BMS (like most Fogstar Drift packs) that communicate charge parameters versus bare cells where you're the BMS, effectively.

On my caddy-based setup I learned this the hard way: I'd set absorption at 14.2V thinking I was being conservative, but my particular cells wanted no more than 3.45V per cell (13.8V pack voltage). Three months of subtle overcharging before I caught it on the Victron app history.

The narrowboat environment adds another layer — temperature compensation matters more when your battery bank is sitting in a bilge that swings 5–25°C seasonally. Make sure BatteryLife is enabled if you're not running a full BMS with DVCC.

@CaddyCamper is right that brand matters — my Fogstar Drift cells on the narrowboat threw a wobbly until I rang Fogstar directly and got the actual recommended absorption voltage, which was slightly different to what the BMS documentation said. Ring the manufacturer, don't trust random PDFs.