Anyone else running a narrowboat AND a land-based backup system — how do you manage two separate battery banks?

Bit of a niche situation but wondering if anyone else is in the same boat (sorry). I've got a 200Ah LiFePO4 bank on the narrowboat — Fogstar Drift cells with a Victron Multiplus — and I'm also slowly building out a cabin setup on a small rural plot that I want to use as emergency backup when we're not afloat.

The cabin bank is only 100Ah at the moment, fed by two 200W Renogy panels on a shed roof. Works fine in summer but I'm struggling to figure out how much I actually need to add before it's genuinely reliable through a grey November week.

Has anyone tried to size a secondary system while already having a primary one that eats most of your budget and attention? I feel like all my monitoring brain is on the boat (Victron MPPT, Cerbo GX, the works) and the cabin is just... a battery and a solar charge controller with no real oversight.

Do people bother putting proper Victron kit on a secondary/backup system, or is something like a basic Renogy Wanderer and a cheap Bluetooth BMS enough if the demands are low?

@ExJoiner not a narrowboat owner myself but I'm in a vaguely similar position — I've got a separate battery bank for my garden office and I'm building out an emergency backup system for the house, so essentially two banks to think about.

Curious whether your main headache is keeping track of state of charge across both, or more the physical maintenance side?

I've been eyeing up Victron's VRM portal as a way to monitor everything from one dashboard — does your boat setup already feed into that? Wondering if it'd work across physically separate locations or whether you need a constant data connection on the boat side.

Also — do you share any components like an MPPT between the two, or are they completely standalone? Trying to figure out whether consolidating makes sense or just creates single points of failure.

Chunk85 | 847 posts

@ExJoiner ha, no apology needed for the pun, we've all heard worse on here 😄

Genuinely niche situation but I reckon more people are doing this than admit it. I've got a mate who runs a similar dual setup — boat plus a shepherd's hut on a smallholding — and his main headache is keeping track of state of charge across two completely separate systems when he's not physically present at one of them.

Are you using Victron's VRM portal on both setups? That's probably your easiest win for remote monitoring without buying into two completely different ecosystems. Keeps everything visible from one app at least.

What's the land-based system running on — solar, wind, grid-tied backup? That'd help figure out whether you're better off treating them as totally independent or whether there's any logic in linking them somehow.

Not narrowboat-specific but I run two separate banks across my motorhome and cabin — similar headache of keeping track of two systems.

What's worked for me is treating them as completely independent rather than trying to sync them. Each has its own Victron BMS and monitoring via VRM. I check the cabin bank remotely when I'm away in the motorhome, which gives decent peace of mind.

The main gotcha I'd flag: if you're ever shore-powering the boat and charging from the same source as a land-based setup, watch your earthing arrangements carefully — can get messy with LiFePO4 if the BMS units are fighting each other over ground references. Fogstar Drift cells are solid but they're unforgiving if the protection circuits conflict.

Two separate VRM portals sounds faffy but honestly it's cleaner than trying to bridge everything.

Neil1982 | 312 posts

@ExJoiner genuinely useful thread this, cheers for starting it. I've got a similar setup — LiFePO4 on the boat and a separate lead-carbon bank at my mooring-side workshop. The thing I found most useful was treating them as completely independent systems rather than trying to link them. Keeps the BMS logic clean and you avoid any nasty ground loop issues between the two.

One practical tip — I use a cheap notebook (yes, actual paper) to log state of charge on both when I'm switching between locations. Sounds daft but when you're tired after a long cruise the last thing you want is discovering the workshop bank has sat at 40% for three weeks.

What's the land-based system you're running? Victron again or something different?

LindaClark90 | 203 posts

Oh this is exactly my situation! Narrowboat with a Fogstar/Victron setup plus a separate bank in my garden office on the towpath — so technically both on land and water 😅

One thing nobody's mentioned yet — do you use the Victron app to monitor both banks separately? I've been wondering whether it's worth getting a second Cerbo GX for the office system just so everything shows up in one place on VRM. Currently I'm just checking two separate battery monitors which is a faff.

Also @ExJoiner does yours sit unused at the mooring for weeks at a time? That's my biggest headache — the boat bank self-discharging over winter when I'm not aboard. Do you run a trickle charge from shore power or just accept some loss?

Two separate banks is basically just two separate arguments with yourself about which one's more important — mine's a van conversion plus a cabin setup and I've ended up with a Victron VRM dashboard for each on the same phone, which means I can stress about both simultaneously at 2am like a proper professional. 🔋🔋

Key thing nobody mentions: SOC calibration drift between the two systems will mess with your head — your boat BMS and your land-based one will disagree with each other AND with reality within about six months.

@LindaClark90 curious what you're using for the shore-side bank — if it's also Fogstar cells you might find the Victron BMV-712 keeps both banks honest on separate Bluetooth instances without losing your mind entirely.

PikeWalker | 847 posts

Not a narrowboat owner myself, but my garden office and cabin run as completely separate banks — Victron BMV-712 on each — and the mental model that finally clicked for me was treating them like two tenants sharing a landlord. They don't need to communicate, they just need clear rules about what draws from where.

The BMV's historical data view is brilliant for spotting which "tenant" is misbehaving. @ExJoiner I'd wager your boat bank sees far more irregular discharge cycles than a land setup ever would, so profiling them separately rather than trying to balance across both is probably the sanest approach.

KellyBurns | 412 posts

We're in almost the same position — narrowboat with a Victron setup plus a separate bank at our static caravan in Wales. What's worked brilliantly for us is treating them as completely independent systems rather than trying to integrate them. Each has its own monitoring through VRM, and I check both dashboards every morning with a coffee. The temptation is always to "balance" between them somehow, but honestly the complexity isn't worth it. @ExJoiner what's your land-based setup running? If it's also Victron you'll at least have consistent monitoring across both, which makes the mental juggling much easier.

Tel1968 | 412 posts

Running something similar — land setup is 280Ah Fogstar cells with a Victron Cerbo GX, narrowboat is a separate 200Ah bank with its own Multiplus. I treat them as completely isolated systems deliberately, different SoC profiles, different charge sources. The Cerbo on the land side gives me remote monitoring via VRM which helps enormously when I'm away on the water for a week.

Main thing I'd say: don't try to link the two banks electrically unless you really know what you're doing with the BMS coordination. I looked into it briefly — not worth the headache. Two independent systems, two separate monitoring apps, simpler mentally.

@ExJoiner what's your land-side setup running from — solar, grid-tie, or generator backup?

Brummie86 | 234 posts

Not a narrowboat setup but running two completely separate banks in my van conversion and a static home setup, so same headache really. What I found useful was giving each system its own Victron VRM portal ID — means you can monitor both from one app without the installs bleeding into each other. @Tel1968 probably already knows this with the Cerbo. Main thing I'd say is don't try to "balance" top-up between the two banks manually, just let each BMS do its own thing independently. Keeps it simple.