Shed office build - worth going bigger on the battery if I'm running monitors all day?

Done this exact calculation for my motorhome setup so it translates pretty well.

Monitors are surprisingly hungry — a couple of decent 27" screens plus a laptop dock can pull 80-120W easy. Running 8 hours that's nearly 1kWh just for the screens before you factor in lighting, a phone charger, maybe a small fan in summer.

My rule of thumb: work out your daily usage, double it, then size the battery for 2 days of that. Sounds excessive but you'll thank yourself on overcast weeks in November when the panels aren't doing much.

If you're going lithium (and you should, shed office is a perfect use case), the price difference between say 100Ah and 200Ah is rarely as dramatic as people expect. Fogstar Drift is decent value if budget is a concern. Victron if you want the ecosystem to grow with you.

Few things worth nailing down first though:

• How many monitors exactly, and what size/type?
• Any plans for a small heater or just a heated mat?
• What's your panel situation looking like?

Heating is the wildcard that changes everything — even a modest 400W oil-filled rad will dwarf your monitor draw. If that's on the cards, I'd say go bigger without hesitation.

What inverter are you thinking? That'll affect your options too. Would be good to hear what others have done with shed builds — I've been tempted to do a proper garden office myself rather than keep living out of the van!

@SuffolkSolar that's really useful context from the motorhome side, cheers.

I'm planning something very similar for my garden office — probably two 24" monitors plus a mini PC. A few things I'm not sure about:

• Does the depth of discharge you're comfortable with change the calculation significantly? I've been looking at Fogstar Drift LiFePO4 and they're rated to 80% DoD, which feels like it changes the maths vs lead-acid
• Is it worth factoring in winter solar yield as the limiting constraint rather than the battery size itself? My roof orientation isn't ideal
• What did you land on for inverter sizing — did you go pure sine wave from the start or did you regret not doing so?

Trying to decide between a 100Ah and 200Ah Fogstar setup and whether the extra cost is genuinely worth it for daily full-time use.

@SuffolkSolar this is dead relevant to me actually — I've been wrestling with similar numbers for my van conversion and the monitor draw always catches people out.

Quick question though: are you factoring in the inverter efficiency losses on top of that 80-120W figure? Running AC monitors off a 12V bank you're typically losing another 10-15% through the inverter, so your actual battery draw is higher than the screen specs suggest.

Worth asking @Liz1979 too — are your monitors AC or have you looked at 12V/USB-C native displays? I switched to a couple of USB-C monitors on the narrowboat and the difference in consumption was genuinely surprising. Cuts out the inverter entirely for the screens at least.

What battery chemistry are you both planning — LiFePO4 I'm assuming? That usable capacity calculation changes massively vs lead acid.

@SuffolkSolar yeah monitors catch a lot of people out. My van setup runs a single 27" and it's easy to forget idle vs full load difference — screen brightness alone shifts things noticeably.

One thing worth adding for shed builds specifically: you've got more flexibility on battery size than we do in vans, so I'd just go bigger from the off. Fogstar Drift cells are decent value if you're going DIY, or a pre-built Fogstar/Victron combo if you want plug and play.

Also worth factoring in winter — solar yield drops massively in Suffolk in December. Size your battery so you can coast through a couple of cloudy days without stressing it below 20%.

Something I learned the hard way on the narrowboat — don't just size for your average draw, size for your worst day.

Dark November afternoon, heating running, monitors cranked to full brightness, maybe a video call draining the laptop faster than usual. That's when your theoretical numbers fall apart.

I'd go at least 200Ah of usable capacity (so roughly 300Ah if you're running lead, though honestly just go lithium and be done with it — Fogstar's cells have served me well). Pair that with more solar than you think you need on the shed roof.

@ThingamyBob62 is right about idle vs full load catching people out, and I'd add: screen brightness is a massive variable nobody mentions. Drop from 100% to 60% brightness and you can shave 20-30W off your total draw without really noticing.