Anyone know if a 200Ah lithium battery is overkill for just powering a shed?

So I'm in a similar boat and been wrestling with this exact question for weeks now.

My setup at the moment is a 100Ah Fogstar Drift sitting in the motorhome, but I'm looking at doing a small off-grid shed for a hobby space — basically running LED strip lighting, a phone charger, maybe a small Bluetooth speaker, and occasionally a soldering iron (roughly 50W). Nothing wild.

I keep reading that you should only draw down to 20% on lithium, so effectively you're working with 80Ah usable on a 100Ah battery. For my load calc, I'm nowhere near pushing that daily.

But here's what's got me second-guessing:

• My shed gets very little direct sun in winter (north-facing roof, surrounded by trees on two sides)
• I'd probably only be out there a few times a week
• Tempted by the 200Ah Fogstar or even a Renogy option just for the peace of mind that I'm not constantly near empty after a cloudy week

Is the 200Ah genuinely worth the extra cost, or am I better putting that money into better solar input instead? Someone on another thread mentioned that more panel wattage solves the "thin winter days" problem better than bigger storage, which made a lot of sense to me — but I'd love to hear from anyone who's actually run a low-draw shed setup through a UK winter before committing.

What did your actual real-world experience look like?

Hey @Nessa68! Really depends what you're running in the shed to be honest. For basic lighting and maybe charging tools, a 100Ah lithium is usually more than enough - you'd only be using a fraction of it daily. The 200Ah starts making sense if you're running power tools for extended periods, a small fridge, or anything with a decent continuous draw.

Worth doing a rough load calculation first - jot down everything you want to power, the wattage, and roughly how many hours per day. Multiply those together and that gives you your daily Wh requirement. Then size your battery so you're not regularly draining below 20-30% even in poor weather.

The Fogstar Drift you've already got is cracking quality, so if you go that route again you won't be disappointed! What are you actually planning to run in there?

Depends massively on what you're calling "basic" tbh. I've got a garden office running off a 200Ah and it's honestly not overkill at all once you factor in monitors, a small heater, kettle etc. Even a humble 100Ah disappears fast on cloudy days with minimal solar input.

Worth doing a rough load calc first — add up your daily Wh consumption and work backwards. There's a decent calculator on the Victron site that helps.

Also remember with lithium you're only realistically using ~80% usable capacity, so a 200Ah isn't really 200Ah in practice. If budget allows, go bigger — you won't regret it. Upgrading later costs more in the long run.

@Nessa68 Worth running a proper load audit before committing — add up your wattage draws and multiply by daily hours, then divide by your battery voltage to get Ah consumption. A 200Ah LiFePO4 is realistically usable down to about 20% SOC, so you've got 160Ah working capacity.

For a basic shed (LED lighting, phone charging, maybe a small inverter occasionally) you might genuinely be fine with 100Ah — similar spec to your Fogstar Drift, which is a solid unit. I run a comparable setup as emergency backup on my boat and 100Ah handles overnight loads comfortably.

That said, lithium doesn't suffer from partial state-of-charge like lead-acid does, so oversizing doesn't actually hurt the battery. If budget allows and you anticipate expanding the shed's usage, the 200Ah gives you headroom without penalty.

Got a static caravan running off a pair of 100Ah Fogstar Drifts in parallel and honestly wish I'd just gone 200Ah in a single unit from the start. Less faff with balancing.

But for a shed specifically — what's actually going in there? That's the bit nobody's answered yet. LED strip lighting and a phone charger is very different to a bench grinder or a compressor.

Also worth considering: are you on solar, mains top-up, or just relying on stored capacity? Because a 200Ah bank with no reliable charging source is going to leave you frustrated pretty quickly come November.

What panels are you planning to pair it with?