Anyone else had their Fogstar Drift cells arrive with wildly different state of charge?

Took delivery of a 16-cell 280Ah LiFePO4 order from Fogstar last week for my Welsh hillside cabin build. Cracked open the boxes to find the cells ranging from about 2.8V all the way up to 3.35V. Nothing catastrophic, but enough to make top-balancing a proper faff before I could even think about wiring them into a 24V bank.

Spent two days nursing them up with a bench power supply at around 0.05C, keeping a close eye on the Victron Battery Protect downstream. Got them all sitting at 3.65V eventually, held within about 5mV of each other — which honestly felt like a small victory. The JK BMS is now seeing a pretty tidy pack.

Just wondering whether this is standard for Fogstar, or whether anyone else has had a similar lottery? Did you contact them, or just crack on with the balancing yourselves? Starting to think I should have documented the incoming voltages more carefully in case it became a warranty conversation.

JasonPhillips | Posts: 847

@MountainBarry Completely normal mate, don't panic. LiFePO4 cells are typically shipped in a partial or varied state of charge deliberately - partly for transport safety regulations, partly just because they've been sitting in a warehouse for different lengths of time since manufacture.

What you'll want to do before assembly is top-balance them all. Charge each cell individually to 3.65V with a bench power supply, hold it there until current drops to near zero (maybe 100mA or less), then let them rest a few hours. Once they're all sitting at the same resting voltage, then wire up your pack.

Don't be tempted to just slap them together and rely on the BMS to sort it out - that can take ages and puts unnecessary stress on the cells early on. Bit tedious but absolutely worth doing properly from the start.

LauraCole | Posts: 312

@MountainBarry As @JasonPhillips says, nothing to worry about. What you'll want to do before assembly is top-balance all your cells. Charge each one individually to 3.65V with a bench power supply, let the current taper right down to practically nothing, then let them rest. Once they're all sitting at the same voltage you can connect them up and let your BMS handle things from there. It's a bit tedious with 16 cells but genuinely worth doing properly — it makes a real difference to long-term pack performance. For a cabin build where you're relying on this kit through Welsh winters, you really don't want to skip this step. Have you got a decent bench supply already, or are you still sorting your kit out?

@MountainBarry pretty normal tbh, Fogstar (and most cell suppliers) ship at partial/mixed SoC for transport safety regs. The 2.8V ones aren't damaged, just sitting low.

Top balance them all before first use — charge each cell individually to 3.65V with a bench power supply, then connect in parallel overnight to let them equalise. Don't throw them straight into a pack and hit them with bulk charge, you'll just stress the weaker cells.

Did exactly this with my van build last year, took a weekend but worth it. After balancing my JK BMS has barely had to do anything since.

@GeoffRobinson is right about the transport regs. What you do need to worry about is top-balancing those cells before you wire anything up properly. Shove them all on a bench power supply or decent charger one at a time, get them all to ~3.65V, then let them sit and settle.

My Fogstar cells arrived in a similar state last year for the motorhome build — looked a right mess on the multimeter. Took an afternoon to sort but the pack's been solid ever since.

Don't let anyone rush you into just slapping a BMS on and hoping for the best. Your BMS will spend its whole life fighting an unbalanced pack. 🔋

EcoFlow_Master | Posts: 847

When my Fogstar order arrived for the static caravan build, I had almost the exact same spread — a couple of cells sitting stubbornly low around 2.9V while others were nudging 3.3V.

What nobody's mentioned yet: don't rush the top-balance. I made the mistake first time round of pushing too quickly with a bench power supply. Slow and steady at around 3.65V per cell, letting the current naturally taper off, made a noticeable difference to how the pack behaved under load afterwards.

Worth logging each cell's voltage before and after — a simple spreadsheet saved me a fair bit of head-scratching when I was commissioning the Victron system later. You'll thank yourself when you're troubleshooting at midnight in a Welsh field in November. @MountainBarry that cabin location sounds familiar territory.

SuffolkDweller | Posts: 312

@MountainBarry agree with what the others have said about the transport regs and top-balancing. One thing worth adding — before you do anything else, give each cell a good visual inspection and log the resting voltage of every single one after they've sat for 24 hours undisturbed. Any cell that's significantly lower than the rest after that rest period could indicate a self-discharge issue rather than just shipping variation, and you'd want to identify that before building your pack. I had one dud cell in a batch a couple of years back that only revealed itself through exactly this method. Also worth checking terminal condition and that none of the packaging caused any pressure damage during transit. Once you're happy with the inspection, then crack on with the top-balance. Good luck with the cabin build — Welsh hillside sounds brilliant!

MountainGary | Posts: 1,204

@MountainBarry that voltage spread is completely normal and nothing to worry about. One thing I'd add that hasn't been mentioned yet - before you start top-balancing, give each cell a few hours to rest at room temperature first. If your Welsh cabin is anything like my setup, those cells may have been sitting in a cold transit van and the resting voltage won't be fully accurate until they've stabilised thermally. LiFePO4 readings can be a bit deceptive when cold. Once they've settled, then start your balancing process. Worth the patience rather than rushing in.

Lefty | Posts: 203

Same thing with my Fogstar cells for the shepherd's hut build — spread was even wider than yours if I remember right. What nobody's mentioned yet: before you do anything else, let them sit at room temp for 24hrs if they've been in a cold van/warehouse. Voltages can read a bit off when the cells are chilled. Then do your top balance properly before connecting the BMS. My JK BMS made the whole process pretty painless once everything was at a stable temp.

EwanLamb | Posts: 847

@MountainBarry before you do anything else, I'd recommend letting all the cells rest at room temperature for 24-48 hours if they've just arrived — especially coming into Wales this time of year. Cold cells can read lower voltages than they actually are. Once they've settled, do a slow top-balance before assembling the pack. I use a bench power supply set to 3.65V with current limited to around 5A per cell. Takes patience but you'll thank yourself later when your BMS isn't constantly fighting an unbalanced pack. Sounds like you've got decent cells there regardless.

LochStu | Posts: 412

@MountainBarry worth noting that the lower voltage cells (your 2.8V ones) aren't necessarily deeply discharged — LiFePO4 has such a flat discharge curve that a small voltage difference can represent quite a significant state of charge difference. Before you start top balancing, I'd give each cell an individual charge to 3.65V using a bench power supply if you have access to one. Makes the subsequent top balance much cleaner and gives you a chance to check each cell's capacity individually. Also log the voltages daily during rest — tells you a lot about cell health early on.

DH_VanLife | Posts: 1,156

@MountainBarry totally normal with Fogstar cells in my experience — mine arrived in a similar state for my Transit build. The key thing nobody's mentioned yet is to top-balance them all before you assemble the pack. Charge each cell individually to 3.65V, let them settle, and get them all sitting at the same resting voltage before connecting them in parallel or series. Skipping this step and relying solely on your BMS to sort it out later causes all sorts of grief down the line. Takes a bit of patience but saves headaches once everything's wired up.