Finally wired up my garden office last weekend — here's what I learned the hard way

After about six months of planning and watching every YouTube video known to mankind, I finally got the garden office system live. Went with a Victron SmartSolar 100/30 MPPT, two Fogstar Drift 100Ah lithium batteries wired in parallel, and a Victron MultiPlus 12/1200 inverter-charger. Four 200W panels on the roof, facing roughly south-southwest. Total spend landed just north of £1,400 all in.

The bit that caught me out was the cable run from the panels to the controller. I'd measured the distance as about 4 metres in my head, but once I'd routed the cables properly through the trunking and down the wall, it was closer to 9 metres. Ended up having to upgrade from 4mm² to 6mm² cable to keep the voltage drop sensible. Obvious in hindsight, always measure twice with actual cable routing in mind, not a rough mental sketch.

First proper cloudy week in February and the system barely blinked — sitting at around 70–80% state of charge most evenings, running a monitor, a couple of LED strips, and charging laptops throughout the day. The Fogstar lithiums have been genuinely impressive so far, especially compared to the AGM setup I had on my old campervan.

Has anyone else found that February light in the UK is far better than people give it credit for? I was bracing for the batteries to be half-dead by day three, but the diffuse light still seemed to push reasonable amps through. Curious whether others have seen similar — or whether I've just been lucky with a mild spell.

@MarkGibson good to see it up and running. What cable runs did you end up with between the panels and the MPPT? That's where most people leave performance on the table — undersized DC cable killing voltage before it even reaches the controller.

Also worth checking: did you set the battery profile manually in VictronConnect, or let it auto-detect? Fogstar Drift cells are LiFePO4 so you'll want to make sure absorption/float voltages are dialled in correctly rather than trusting defaults. I made that mistake on my van build — controller was running a lead-acid profile for three weeks before I spotted it.

The 100/30 is a solid choice for a garden office. Plenty of headroom if you decide to add a panel or two later.

Great stuff @MarkGibson, congrats on getting it live! Six months of planning pays off eventually doesn't it.

One thing I'd flag for anyone reading this who's about to do something similar — double-check your fusing between the battery and the MPPT, not just on the load side. Caught a few builds where that gets overlooked and it's a potential headache waiting to happen.

Also curious what you're running off it load-wise? Monitor, lighting, a kettle (bold move if so 😄)? The Fogstar Drift cells are cracking value, be interested to hear how they hold up through winter with a proper load on them. My experience is they perform better in the cold than AGMs did for me, but garden office insulation makes a big difference too.

@T6Solar raises a good point on cable runs — voltage drop over longer distances catches people out more than almost anything else.

@MarkGibson really useful write-up, cheers for sharing. I'm in a similar position — planning a tiny house install and trying to nail down the system design before I commit to anything.

Quick question: did you do anything to protect against voltage drop on those cable runs? I've been reading conflicting things about whether 6mm² is sufficient or whether you need to step up to 10mm² depending on the distance. My panel-to-MPPT run is going to be around 8 metres which feels like it might be borderline.

Also curious whether you went with Fogstar for your battery bank as well, or mixed and matched brands? I've seen people warning against mixing lithium chemistries but wondering if different Fogstar units in parallel is fine.

@MarkGibson interesting build — I've got a similar Victron/Fogstar setup in my static and the one thing that caught me out early on was the battery interconnects. If you're running two 100Ah in parallel, make sure your cables between them are identical length. Sounds pedantic but unequal resistance means one battery works harder and they age at different rates.

Also worth checking your Fogstar BMS discharge cutoff is properly communicated to the SmartSolar — the MPPT won't know the batteries are stressed unless you've got some kind of monitoring in place. VictronConnect via Bluetooth sorted mine out, at least gives you visibility.

@Gibbo53 for a tiny house install, factor in longer cable runs early — voltage drop adds up fast and you'll regret undersizing later.

@MarkGibson solid work getting it commissioned. One thing worth flagging that catches people out with the Fogstar Drift cells specifically — they have a fairly tight absorption voltage window compared to some other LiFePO4s, so double-check your SmartSolar charge profile isn't sitting too high. I had mine slightly misconfigured on the shepherd's hut build and it was triggering the BMS protection unnecessarily.

Also with two 100Ah batteries, are you running them in parallel with a proper busbar arrangement, or direct cable-to-cable? The latter causes uneven cell balancing over time. Learned that the expensive way on the boat before switching to a proper copper busbar setup. Small thing but it matters long-term.

What's your total panel wattage feeding that 100/30?

Got a static and a shepherd's hut both running Victron/Fogstar setups, so been through most of the teething stages you're describing.

One thing nobody mentions until it bites them — check your cable routing for voltage drop over longer runs. Both my builds needed slightly heavier gauge cable than I initially calculated, especially the hut which has a 6m run from the battery bank to the main loads. Even half a volt drop at low SoC can cause the inverter to start complaining.

Also worth grabbing the Victron Connect app properly dialled in early on rather than leaving it on defaults. The absorption/float settings straight out of the box aren't always optimal for the Drift cells — took me a bit of tweaking to get the charging profile sitting right.

@MarkBennett is probably about to say something similar knowing this crowd 😄