Anyone else running a Fogstar Drift as their narrowboat emergency backup — what's your setup?

Just wired in a Fogstar Drift 12V 100Ah as a dedicated emergency bank on the boat, isolated from the main Victron system so it's untouched until everything else dies — basically my "oh crikey" battery.

Paired it with a small Victron IP65 15A charger on a separate circuit, trickle-fed off shore power when we're moored. Keeps it topped off without me thinking about it, which is the whole point really.

Main question: what are folks using to monitor the emergency bank without integrating it into the main BMS loop? I've got a basic Votronic shunt on there at the minute but it feels like overkill for something I'm supposedly never meant to touch — or is that exactly the point?

@Spud nice idea keeping it fully isolated. I run a similar setup but land-based — Drift 100Ah sat in a dry box in the garage, completely separate from my main Victron/Fogstar bank.

One thing worth thinking about on a boat — self-discharge over long periods. LiFePO4 is pretty low but if that battery's just sitting for months you'll want to top it up occasionally. I've got a simple Victron IP65 charger on a timer doing a monthly top-up on mine, keeps it honest.

Also worth checking your low-temp cutoff — LiFePO4 doesn't like charging below freezing, and a narrowboat in January could easily catch that out.

What are you planning to power from it if the main system goes down?

Great thread @Spud! I've got a Drift 100Ah doing something similar on our boat, though mine's semi-integrated rather than fully isolated — it sits on its own bus bar with a manual isolator switch I can throw if the Victron bank gets low or goes wrong.

One thing worth mentioning: the Drift's low-temperature cutoff has saved me grief over winter mooring. When our main bank got sulphated last February and we were running on the emergency setup for a few days, I wasn't worrying about charging it in cold snaps the same way I would with older lithium cells.

Do you have a dedicated small charger keeping it topped up, or are you genuinely leaving it completely untouched? I keep mine on a trickle via a separate solar panel precisely because I'd hate to reach for it in a crisis and find it's self-discharged down to nothing!

@Spud curious what you're using as the isolation switch — is it a manual rotary cutoff or have you automated it somehow?

I've been thinking about doing something similar on my setup (land-based solar rather than a boat, but the principle's the same). My main concern would be the Drift sitting at partial state of charge for months if it never gets called upon — does it self-discharge noticeably over time, or do you have a trickle feed keeping it topped up?

Also wondering whether 100Ah is actually enough for a genuine "oh crikey" scenario on a narrowboat — what loads are you planning to run from it, and for how long?

@Spud my garden office Drift sits on a shelf judging my main Victron system like a disappointed parent, waiting for the day it finally gets to say "told you so."

Love this idea @Spud — I've been thinking about doing exactly this on our 60-footer.

One thing worth considering with the Drift as a pure standby unit is keeping it on a trickle maintenance charge so you're not reaching for it in a crisis and finding it's self-discharged down to 70% over six months of neglect. I've got a small dedicated solar panel (just a 20W jobbie) permanently float-charging mine through a basic PWM controller, completely separate from the main Victron setup.

@AlanPalmer57 — I went for a manual Victron battery protect on mine rather than a rotary, means I can also set a low-voltage cutoff so you can't accidentally flatten it completely if you're running on it for an extended stretch.

@VoltBarry that "disappointed parent" description is absolutely perfect 😄