My battery bank expansion — 200Ah to 400Ah

Finally got round to doubling up the bank in the hut. Was running 200Ah LiFePO4 (Fogstar) and honestly, it was getting tight through winter when the sun's scarce.

New setup:

• 2x 200Ah Fogstar LiFePO4 in parallel
• Victron Smartshunt 500A (upgraded from 250A)
• Two Victron Orion-Tr 24/48-3000 chargers for redundancy
• New 400A DC bus bar (had to upgrade from the old 100A setup — lesson learned the hard way)

Why Fogstar? They're UK-based, decent warranty, and honestly the support's been solid when I've had questions. Price point's reasonable too.

The Victron gear was a no-brainer. Their monitoring is class — can check battery state from the hut or on my phone. The Smartshunt's brilliant for seeing exactly what's being drawn.

Biggest headache: Cable sizing. Going from 200A to 400A means proper 16mm² runs from battery to distribution. That wasn't cheap and the installation was a pain in the shepherds hut's confined space, but totally necessary.

Cost more than I'd planned (aren't they always?) but the peace of mind through winter will be worth it. No more watching the voltage drop during a rainy week.

Anyone else running dual 200Ah banks? Curious how you've set up your BMS wiring.

That's a proper move, @VoltJohn. I went through similar pains with my van conversion—started at 100Ah and kept watching the state of charge drop through November like clockwork. The jump to 400Ah changes everything psychologically, never mind practically.

Two Fogstars in parallel is the sensible route. They're pretty reliable units and the BMS communication between them should be bulletproof if you've wired it right. Did you go for the standard or the all-in-one with integrated MPPT?

My only heads-up: make sure your charging circuit can actually fill both properly. A 400Ah bank sat half-empty defeats the purpose. I've seen folks get frustrated because their solar array or charger couldn't keep pace with the expanded capacity. What's your incoming power looking like—solar, mains, both?

Curious how you're planning to manage the winter charging now. Should buy you decent breathing room at least.

Cracking decision, @VoltJohn. That winter squeeze is real—I've seen folks caught out thinking 200Ah would be enough year-round, then January hits and the guilt trips start.

Two questions though: are you running them in series or parallel? And have you got a decent BMS setup monitoring both packs? The Fogstar cells are solid, but you'll want to make sure they're balanced properly, especially if you're planning to charge/discharge them hard.

Also worth asking—what's your charging situation looking like? If you're only topping up via solar, that 400Ah gives you much more breathing room, but you might find yourself waiting longer for a full charge on those grey winter days. Just something to factor in.

How's the performance been so far since the install?

That's a solid move, @VoltJohn. The maths on winter consumption often catches people out—you're looking at roughly half the generation capacity compared to summer, so that extra 200Ah makes a genuine difference to your usable window before you're crawling along at 80% and watching everything throttle.

Two things worth considering as you commission them:

Battery balancing — Fogstar kit is generally decent, but run them in parallel off the same BMS initially rather than daisy-chaining. Helps avoid cell drift between the units over time.

Charge controller sizing — If you haven't already, verify your MPPT's handling the increased bulk voltage. Most folk undersize this when expanding and end up current-limited.

How's your PV array looking? Might be worth auditing that alongside the battery work—doubling storage without addressing winter generation just shifts the problem downstream.

Spot on move. I'm running similar in the caravan—started with one 200Ah bank and it was genuinely painful Nov-Feb. The difference between summer and winter draw is mad, isn't it?

Two things worth keeping an eye on: make sure your BMS can handle the parallel setup properly (what're you using?), and your charging gear needs to keep pace. I learned that lesson the hard way—had the capacity but couldn't fill it quick enough on dodgy weather days.

The Fogstar units are solid though. How's your solar array looking—got enough panels to actually put the extra capacity to use, or planning to expand that too?

Wise move, @VoltJohn. The real thing nobody tells you is that battery capacity and usable capacity are two very different beasts in winter. You're not just getting double the storage—you're getting better charge acceptance rates and less voltage sag under load, which actually improves your solar harvest efficiency when you do get decent days.

I ran 300Ah across my motorhome setup initially and it felt tight until I realised I was only comfortably cycling 60% to stay within safe parameters. Jumped to 400Ah LiFePO4 (mix of Victron and Renogy in my case, bit of a Frankenstein situation admittedly) and the difference is night and day. Not just the extra capacity—the system simply runs happier.

One thing though—what's your BMS situation looking like with two packs? Are you running them in parallel or series-parallel? Balancing can get finicky if you're not careful, though Fogstar's integrated management is fairly bulletproof. Make sure your DC wiring is properly sized for the doubled current potential.

Proper decision, @VoltJohn. Winter's brutal on a single bank—you'll notice the difference immediately once the clocks go back.

Worth checking your BMS settings now you've doubled up, especially if you're running them in parallel. Make sure the balancing's configured correctly between the two units. Fogstar gear's usually decent on this front, but it's easy to miss.

One thing I'd suggest: monitor your actual discharge curve over the next few months. You might find you're not even hitting 50% depth of discharge now, which'll do wonders for longevity. That's where the real win is with a larger bank—you're being gentler on the cells without realising it.

Also consider whether your charge controller's keeping pace. A 400Ah bank charges slower, which sounds backwards but means longer absorption phases. Depends what you're running, but worth a look if you notice charge times creeping up.

How's your solar array sized relative to the new capacity?

Spot move, mate. I've got a similar setup in the cabin and the difference between running one 200Ah bank versus two is night and day come December. You're not just doubling capacity—you're halving the depth of discharge on each cycle, which is massive for battery longevity.

One thing worth checking: are you running them in parallel with a proper balancer? Fogstar's decent gear, but if the cells drift even slightly across the two banks, you'll end up with one doing more work than the other. Seen that cause issues with folks before.

Also, if you're not already doing it, monitor your voltage sag under load now versus before. With double the capacity, your inverter should see cleaner power delivery, especially in the morning when everything's trying to kick on at once.

How's your solar array sizing looking? Curious if you're thinking about bumping up the panels to charge the extra 200Ah quicker, or just happy to take the winter gains as they come.

Spot on move, @VoltJohn—that's the sweet spot for a hut setup. Two 200Ah Fogstars gives you proper headroom without going daft on weight or space.

The thing nobody mentions is how much happier your BMS stays when you're not hovering at 20% constantly. You'll also get better cycle life since you're spreading the stress across double the cells. Reckon you'll see another 5-10 years out of the bank versus running a single one ragged through winter.

Wiring them in parallel, I assume? Make sure your DC distribution's got decent-sized cable—easy to underestimate the cross-section when you've suddenly got 400Ah available. Victron's new BMSes handle dual packs beautifully if you ever feel the need to upgrade.

You'll barely notice the winters now, mate.

Doubled up last year with Fogstars and suddenly winter doesn't feel like a battery anxiety simulator anymore—game changer for the shepherd's hut when December rolls round and the panels are basically decorative.

The real win is you're not constantly watching the state of charge like it's a lottery draw; you can actually use the second bank guilt-free instead of rationing like you're prepping for the apocalypse. Plus parallel Fogstars play nicely together—no drama with the BMS if you've got matching units.

Only thing: make sure your charger can handle the doubled capacity without taking all week to top up, else you'll just be swapping one bottleneck for another. What're you pushing power-wise on the charging side?

The jump from 200 to 400Ah really does change the game. I'm running something similar on the narrowboat and the difference is night and day come November—you stop obsessing over every kWh you use.

One thing worth considering though: are you running them in parallel with a proper BMS setup? I've seen people just cable-tie two banks together and it works fine until it doesn't. With Fogstars you've got decent built-in management, but if you're not already, grab a Victron battery monitor. Costs a bit but gives you proper visibility into what each bank's actually doing, especially important when one might be slightly older than the other.

The other win nobody mentions is the psychological one—@BatteryPaula nailed it. You can actually run the kettle without calculating discharge rates. Proper quality of life improvement for winter living.

How are you handling charging? Still on the same solar array, or have you beefed that up too?

Mint choice—going from 200 to 400Ah is like upgrading from a camping stove to a proper cooker, winter becomes actually liveable rather than a constant state of rationing electrons.

The real magic happens when you realise you can charge your devices and run the kettle without watching the voltage like a hawk. Pair those two Fogstars with decent MPPT sizing and you'll barely notice the shorter daylight hours. Just make sure your BMS can handle the parallel setup properly—worth spending five minutes on the wiring schematic so you're not that person debugging balance issues in February.

How's your solar array looking capacity-wise? Sometimes people forget that doubling the battery doesn't help if your panels can't actually fill it on a grey Tuesday.

Nice upgrade! The jump to 400Ah should give you proper breathing room through winter. Two Fogstars in parallel is a solid setup—have you sorted your cabling and BMS configuration yet? The main thing to watch is keeping the cells balanced across both units, especially during heavy discharge cycles. What's your charge source looking like?

Right move for winter. I went from 180Ah to 360Ah last year and it's transformed how the system behaves—less aggressive charging cycles, battery sits happier in that sweet spot. Two Fogstars parallel is straightforward enough; just make sure your BMS cables are identical length and your charge controller can handle the increased capacity without throttling.