4x 12V 280Ah or 1x 48V 100Ah help it make sense.

So I'm trying to wrap my head around battery bank configurations for my garden office build and the maths is melting my brain a bit.

I've seen cheap 12V 280Ah LiFePO4 cells going for decent money on eBay (Fogstar occasionally has similar), and I keep seeing people wiring 4 of them in series for a 48V system. That gives you 280Ah at 48V which is roughly 13.4kWh usable (assuming ~95% DoD on LiFePO4).

Then on the other hand there are purpose-built 48V 100Ah batteries — all-in-one BMS, rack mount, tidy wiring — but that's only 4.8kWh.

Obviously they're not really comparable on capacity but the price per kWh on the 4x 12V route looks significantly better on paper. My office only needs to run monitors, lighting, and a small fan heater occasionally, so I'm probably overshooting on capacity either way.

My actual questions:

• Is the 4x series wiring genuinely as straightforward as it looks, or are there hidden gotchas?
• Do I need a separate BMS for each 12V cell, or does one handle the whole series string?
• Anyone had balancing issues across cells from mixed batches?

Running a Victron MPPT and planning a Multiplus-II so compatibility isn't the concern — more about whether DIY series banks are worth the faff vs a plug-and-play unit.

Anyone done this comparison properly or got a series bank running in a similar setup?

@WattHamish both options are ~3.3kWh usable, but the 48V system wins on efficiency, thinner cable runs, and inverter choice — your Victron Multiplus options open up massively at 48V.

Four 12V batteries wired in parallel is a wiring nightmare waiting to bite you, balancing issues, higher current = fatter (expensive) cable, and most decent inverter-chargers prefer 48V anyway.

The "cheap" 280Ah cells aren't cheap once you add a proper 48V BMS, busbars, and cable that won't melt.

For a static garden office build there's genuinely no reason to fight 12V — that's motorhome/van territory where I live and even I'm migrating my rig toward 48V when the Fogstar cells eventually give up.

Something I keep wondering about with these comparisons — does the depth of discharge work out exactly the same between the two configs in real-world use?

Like, my emergency backup setup is 12V and I'm always nervous about the BMS cutting out unexpectedly at low charge. Would a 48V system's BMS be more "aware" of cell-level issues across the bank, or is it essentially the same protection logic just at a higher voltage?

Also @WattHamish — are those 280Ah cells grade A or are you seeing mixed grades on the listings? I've noticed Fogstar and others are quite transparent about cell grading, whereas some cheaper imports seem vague. That would affect my decision more than the voltage question honestly.

Hey @WattHamish, to answer @SunnyNomad's question — yes, DoD works out the same between the two configurations because you're still dealing with the same cell chemistry underneath. LiFePO4 is LiFePO4 regardless of how you string them together. The 48V pack isn't somehow "harder" on the cells than a 12V setup.

One thing nobody's mentioned yet — if you're going the 4x 12V route, make sure your BMS situation is sorted properly. You either need a good quality 12V BMS per battery or a single 48V BMS across the whole bank. Mismatched BMSs on series-connected batteries can cause real headaches with balancing. For a garden office build I'd honestly lean 48V from the start — retrofitting later when you want to add panels or a bigger inverter is a right faff.

@SunnyNomad @24V_Nerd worth adding though — whilst the usable kWh is technically equivalent, in practice your 48V system will squeeze slightly more out of that capacity because you're losing less to heat in the cabling and inverter conversion. On my narrowboat I run 48V and the difference versus my static caravan's old 12V setup is genuinely noticeable in efficiency terms.

Also @WattHamish — consider BMS options. A decent 48V BMS (Victron Lynx Smart BMS plays nicely here) is one unit to monitor rather than juggling multiple 12V units. Fewer points of failure matters when you're relying on it daily.

The 12V route only really makes sense if your loads are predominantly 12V native IMO.