Anyone else running a Victron SmartSolar on a narrowboat? Struggling to get my battery profile right

I've had a Victron SmartSolar MPPT 100/30 on my narrowboat for about three months now, paired with two 200W panels on the roof and a 200Ah AGM bank. On a decent sunny day I'm seeing around 25–30A coming in, which feels about right, but I'm not confident my charge profile is set correctly for the AGMs and I'm worried I might be undercharging or, worse, gassing them.

The batteries are Numax CXV35MF leisure AGMs. Victron's VictronConnect app has a generic AGM preset but I've also seen people say you should dial in the exact voltages from the manufacturer's spec sheet. My current settings are 14.7V absorption, 13.8V float, with absorption time set to adaptive. The batteries are about 18 months old and still seem healthy, but I want to make sure I'm not shortening their life.

The boat is on the cut most weekends and I live aboard full-time from May to September. My main loads are a 12V compressor fridge (about 4–5A average), LED lighting, a Webasto diesel heater fan, and occasionally a small inverter for a laptop. So it's a reasonably busy system.

Has anyone with a similar setup got a profile they'd recommend, or found that the Victron defaults are actually fine for most leisure AGMs? Also curious whether anyone's using a BMV-712 alongside — I'm considering adding one for proper state-of-charge monitoring.

@DailyConvert what AGMs are you running? That makes a big difference to the profile.

On my narrowboat I've got a 200Ah Elecsol carbon AGM bank — had to tweak the Victron presets quite a bit from defaults to stop them cooking.

Key things I'd check:

• Absorption voltage — 14.7V is often too high for boat AGMs sitting in a warm engine bay
• Float — drop it to 13.5V, not 13.8V
• Absorption time — use the adaptive setting, don't fix it

Also worth enabling the battery temperature sensor if your MPPT supports it. Bilge temps vary massively and compensation matters more than people realise.

What are your current voltage settings? Screenshot from VictronConnect would help diagnose it properly.

Hey @DailyConvert, welcome to the narrowboat solar club! One thing worth checking is your absorption voltage — many AGMs want 14.4–14.7V but some cheaper banks are happier around 14.1V. Running too high for too long will cook them.

Also, are you using the VictronConnect app to monitor charge cycles properly? The tail current setting is often overlooked — I'd suggest dropping it to around 2% of your battery capacity (so roughly 4A for your 200Ah bank) to make sure absorption ends correctly rather than timing out prematurely.

With 400W of panels on a 200Ah bank you've got a decent ratio, so you should be getting full charges on reasonable days. What does your State of Charge look like by mid-afternoon on a sunny day? That'd tell us a lot about whether the profile is actually the issue.

@DailyConvert my garden office runs a SmartSolar 100/30 too (different use case but same controller quirks). One thing nobody's mentioned — check your absorption time isn't set too aggressively. Victron's default adaptive absorption can be overly long for AGMs, cooking the batteries slowly over weeks.

In VictronConnect, try setting a fixed absorption time of around 2 hours max rather than letting it calculate adaptively. AGMs don't need prolonged absorption the way flooded lead-acid does.

Also worth enabling the BatteryLife algorithm if you're not already — it's buried in the settings but it genuinely extends AGM lifespan by preventing chronic undercharge, which is the real killer on a liveaboard where usage patterns vary wildly day to day.

What firmware version are you on? Some older builds had dodgy absorption behaviour that was fixed later.

Not a narrowboat setup but I run a SmartSolar 100/20 in my shepherd's hut so similar ballpark.

One thing nobody's mentioned — check your tail current setting in VictronConnect. Most AGMs want absorption to end when current drops to around 2–4% of bank capacity, so roughly 4–8A for a 200Ah bank. Factory default is often way off for smaller setups.

Also worth enabling the battery temperature sensor if you haven't — AGMs hate being overcharged in summer, and absorption voltage really should drop as temps rise. The SmartSolar handles this automatically once it's got a proper temp reading.

What's your float voltage set to? Anything above 13.5V on AGM long-term is asking for trouble with water loss.

Got a SmartSolar on my motorhome AND a shepherd's hut so I've basically paid Victron's mortgage at this point — for AGMs the thing that sorted mine was enabling the equalization cycle every 30 days or so, because without it the bank slowly sulks like a British summer. Also worth grabbing the VictronConnect app and logging a week's worth of data before you tweak anything, otherwise you're just guessing in the dark (literally, if it goes wrong). @JLB_Boats is right that temperature compensation matters more than most people think — my hut's battery was being charged like it was in the Sahara all winter.

Great thread! Three months in is about the right time when you start questioning your settings after seeing how the system actually behaves through different weather.

One thing worth checking specifically for narrowboat use — if you're cruising regularly, your alternator is doing some of the charging work, and the SmartSolar may be picking up mid-cycle rather than starting from a proper absorption phase. This can mess with how the controller interprets your battery state.

In VictronConnect, have a look at your history tab and check whether absorption time is being cut short on days when you've been running the engine. You might benefit from enabling the "BatteryLife" algorithm if you're not already using it, which handles partial state of charge situations better than a fixed profile.

What absorption and float voltages are you currently running for the AGMs? That'd help narrow things down.