Anyone else running Fogstar Drift cells in a garden office setup? Sizing questions inside

Last year I put together a 200Ah 12V bank using four Fogstar Drift 200Ah LiFePO4 cells with a Daly BMS. It's been powering my garden office pretty reliably — lights, a small monitor, laptop charging, that sort of thing. But I'm starting to wonder if I've undersized it, especially heading into winter with shorter days and the occasional need to run a small fan heater as backup.

My solar input is 400W through a Victron SmartSolar 100/30, and I'm grid-tied for top-up charging when needed. The thing is, I've noticed the BMS cutting out occasionally when I push consumption above about 800W — I suspect the Daly's continuous discharge rating might be the weak point rather than the cells themselves.

Has anyone swapped out a Daly for a JK BMS on a similar cell configuration? I've seen them recommended a fair bit on here. Also open to thoughts on whether doubling to 400Ah makes sense for emergency backup purposes — I'd want at least a couple of days' autonomy if the grid goes down.

DazBarker93 | Posts: 847 | Location: Yorkshire

Hey @Tina1971, nice setup! The Drift cells have a solid reputation on here for the price point. One thing worth checking with your Daly BMS — what's the continuous discharge rating you've got set? Some of the cheaper Daly units can be a bit conservative with their protection thresholds and occasionally trip unnecessarily under brief surge loads, like when a laptop charger kicks in cold.

Also, what's your charging source? If you're on solar, make sure your MPPT is properly configured for LiFePO4 absorption voltage (around 3.45-3.65V per cell, so roughly 13.8-14.6V at 12V system level). Fogstar recommend staying below 3.65V per cell to keep cycle life healthy long term.

What's the actual question on sizing — are you thinking of expanding the bank?

SolarKeith | Posts: 312 | Location: Array

@Tina1971 Four Drift cells and a Daly BMS in a garden office is basically the off-grid starter pack at this point — if you find yourself needing more capacity, the Daly does handle 8S expansion without too much drama, though I'd be tempted to jump to a Victron SmartShunt at that point just so you've actually got visibility into what your bank's doing rather than vibes-based guesswork.

WezBrown66 | Posts: 1,203 | Location: Shropshire

Nice one @Tina1971 — similar setup here in my workshop, though I went slightly larger. One thing worth considering if you're thinking about expanding: the Drift cells respond really well to a quality charger with proper LiFePO4 absorption settings. I found my Victron IP65 made a noticeable difference to how consistently the cells balanced compared to my old generic unit.

What's your solar input looking like? Garden offices can be sneaky with consumption once you start adding small creature comforts — a fan heater in winter absolutely murders a modest bank. If you're regularly pulling it below 50% SoC, bumping to a 300Ah bank might be worth pencilling in for next year. The Drift cells are competitively priced enough that it's not a massive stretch. What's your typical daily usage looking like roughly?

FinnRobinson | Posts: 456 | Location: Lincolnshire

Great setup @Tina1971! One thing worth keeping an eye on with the Daly BMS — they can be a bit conservative on their balancing thresholds, so if you notice any cell drift over time it might be worth grabbing a cheap active balancer to run alongside it. Makes a noticeable difference with the Drift cells in my experience.

Also curious what your solar input looks like? Garden offices in the UK can really struggle through November–February, so knowing whether you've got adequate panel wattage and a decent MPPT controller will help folk here give you better advice on sizing if you're thinking of expanding. What's the actual sizing question you had in mind? Think your message got cut off!

MPPTFan | Posts: 847 | Location: West Yorkshire

Nice build @Tina1971! The Drift cells have a solid reputation and you've sized it sensibly for that kind of load.

One thing nobody's mentioned yet — have you got any cell-level monitoring set up? The Daly BMS will protect you, but it won't always give you great visibility into individual cell voltages drifting apart over time. Something like a cheap Xiaoxiang BMS app via Bluetooth, or even just a periodic manual check with a multimeter, can catch any imbalance before it becomes a problem.

Also worth knowing your actual usable capacity once you factor in not regularly dropping below 20% SOC — you're realistically working with around 160Ah day-to-day, which should still be plenty for your described loads. How are you charging — solar, mains, or hybrid?