Sizing a battery bank for a garden office — 24V vs 48V worth the hassle for 2–3kWh usable?

Currently speccing up a standalone system for a 10×12ft timber office at the bottom of the garden. No mains connection — not worth the trenching cost across 40m of established lawn. Daily load is roughly 400–600Wh: a laptop, two monitors, some LED lighting, a small fan heater on a thermostat (only kicks in occasionally), and a mini fridge. Using a Victron SmartSolar MPPT 100/30 I had spare, with 600W of panels on a south-facing lean-to roof.

The question is battery voltage. I was leaning toward 24V to keep cable runs manageable (office is about 8m from the panel array combiner box), but a couple of people on other threads have suggested going straight to 48V given the Victron MultiPlus-II 48V units are now pretty competitively priced and losses are lower. For 2–3kWh usable storage, is the added complexity of a 48V bank actually justified, or is 24V perfectly sensible at this scale? I'm looking at either Fogstar Drift 24V 100Ah LiFePO4 units or building a 48V bank from Fogstar's 12V 100Ah cells in series — though that latter option feels like more BMS headache than I want.

Also curious whether anyone's running a Cerbo GX in a setup this small — seems like overkill but I do like the monitoring granularity, especially for a structure that'll sit unattended for days at a time in winter.

LiamWalker | 847 posts

@Taffy29 For 2–3kWh usable I'd honestly push towards 48V without hesitation. The wiring savings alone make it worthwhile — you're running thinner cable at lower current, which matters when you're routing back to solar panels. At 24V you're doubling the current for the same wattage, meaning heavier (and pricier) cable runs and more heat.

The "hassle" argument gets overstated. Most decent inverter-chargers these days are 48V native and frankly better value than their 24V equivalents at that capacity range. Victron Multiplus-II 48/3000 is the obvious candidate.

Battery options open up nicely too — 16 x 280Ah LiFePO4 cells wired 16S gives you a clean 48V pack if you're going DIY route.

What's your panel situation? South-facing roof on the office itself, or ground-mounted?

HiluxLife | 312 posts

@Taffy29 48V all day — my narrowboat taught me that undersizing voltage is the gift that keeps on taking, usually right when you're trying to run something important on a grey Tuesday in November. Fogstar Drift 48V cells are practically garden-office shaped at this point, and your Victron kit will thank you for not forcing it to push serious amps down skinny cable. 2–3kWh usable on 24V works, but so does paddling a canal boat with a spoon.

Louise1984 | 312 posts

Ran a very similar setup for my garden office — ended up on 48V with a Victron MultiPlus-II 48/3000 and two Fogstar Drift 48V 100Ah batteries. For the load you're describing, 48V just makes everything cleaner. Thinner cable runs, cooler connections, less fuss overall.

One thing I'd add that hasn't been mentioned: factor in your worst-case winter days carefully. My office faces northeast and I genuinely underestimated how little the panels pull through November–February. I ended up adding a third battery rather than more panels — easier to fit in the space.

If budget is tight, 24V works, but you'll likely regret it once you start adding loads.

RobJones85 | 203 posts

Done similar sizing calcs for my motorhome build so know this space reasonably well. One thing nobody's mentioned — at 2–3kWh usable you're probably looking at 4–5kWh nominal with LiFePO4 (Fogstar Drift cells are worth a look for static installs, decent price per kWh).

At that capacity 48V genuinely makes sense purely on BMS and cell balancing grounds, not just cable savings. Smaller parallel strings = fewer headaches long term.

One genuine 24V argument though: secondhand inverter/charger options are far more plentiful and cheaper. If budget's tight, a quality used 24V Victron Multiplus beats a budget 48V unit every time.

What's your planned solar input? That might actually be the deciding factor here.