Building My Own 6kW Solar + 25kWh Battery System – Full DIY Build”, “POWMR 6kW Solar & 25kWh Battery Build – From Start to Finish

Following this closely — just finished a similar build myself but only got to 15kWh with a Fogstar Drift 48V setup, so 25kWh is proper ambitious 👀

Curious about your cell choice. Going prismatic LiFePO4 I assume? What BMS are you running? I messed about with a cheap JK BMS first and honestly it was fine until it wasn't — ended up swapping to a Victron Lynx Smart BMS which plays nicely with my Multiplus II and gives me proper comms through VRM.

Few things I'd flag from my build:

• Cell balancing before first charge — took me ages, don't skip it
• Busbar sizing — I underestimated this and got warm connections under load, not ideal
• Fusing at each battery — learned this one the hard way during a fault

Also — what inverter are you pairing the POWMR with? I've not used one personally but seen mixed reviews on sustained output vs peak ratings. Might be worth stress testing it properly before you rely on it for anything critical.

On the solar side, 6kW is a solid array. String config or doing anything with optimisers? In the UK you'll want every bit of that on gloomy days, obviously 😅

Stick some photos up as you go — half the reason I'm on here is to live vicariously through other people's installs while I plan my next expansion. Got EV charging running off mine now which has been a game changer.

@DownsExplorer nice work on the 15kWh Fogstar build — the Drift is a solid unit for a plug-and-play solution. Jumping to 25kWh with prismatic LiFePO4 cells is a different beast altogether though, especially on the BMS side of things.

What cells are you looking at? EVE and CATL grade A prismatic are the usual go-to for DIY builds at that capacity. Biggest thing people underestimate is cell matching and initial top balancing — gets tedious fast with a large pack but absolutely worth doing properly before you commission anything.

Also worth thinking about your BMS communications early on if you're pairing with a POWMR inverter — some of them play nicer with certain protocols than others. What comms setup are you planning?

@DownsExplorer what BMS are you running with the Fogstar Drift setup? Curious whether you went with the built-in management or added an external layer — I've been weighing up something similar for my motorhome but 25kWh feels like overkill for my use case.

For prismatic cells at that scale, are you sourcing direct from EVE or CATL, or going through a UK distributor? Import duty and shipping costs seem to swing the maths considerably depending on batch size. Also wondering what cell-to-cell balancing tolerances you're working to before first charge — I've read some conflicting advice on whether to passive balance at storage voltage or push to full before paralleling.

@DownsExplorer 25kWh in a static caravan is exactly where I ended up after starting "modest" too. Word of warning from painful experience — at that capacity, your BMS choice becomes absolutely critical, not an afterthought. I ran a JK BMS on my 280Ah EVE cells and the active balancing made a genuine difference over weeks of partial-state cycling in poor Scottish weather.

Also worth thinking hard about your busbars and cell compression now, before you're pulling everything apart six months down the line. Prismatic cells will swell slightly through charge cycles — proper compression boards saved me a rebuild.

What inverter are you pairing this with? At 6kW you'll want something that talks properly to your BMS, or you're flying blind on protection.

@DownsExplorer 25kWh prismatic is the way to go if you've got the space. I'm running a similar capacity across my shepherd's hut and boat builds — different configurations but same EVE 280Ah cells throughout. The key thing nobody mentions early enough is busbar sizing and cell compression. Prismatics absolutely need proper compression fixtures; without it you'll see capacity fade within a year as the cells swell unevenly. I fabricated aluminium end plates with threaded rod and foam padding — cost maybe £40 in materials but made a huge difference to cell consistency during balance cycles. Also worth torquing your terminals properly with a calibrated wrench — EVE spec is 4Nm, people consistently over-tighten and damage the threads. What cells are you going with specifically, and have you sorted a Victron Cerbo for comms yet?

@LutonCamper shepherd's hut gang represent 🛖 — mine's basically a battery with a bed in it at this point.