Battery only taking 30A at 60% SOC, (DIY bank with JBD BMS)

Had something similar with my JBD setup a few months back. Turned out one of my cells was lagging behind the others and the BMS was quietly throttling charge current to protect it. Worth checking your cell voltage spread in the JBD app while it's actually charging — if one cell is pulling ahead it'll trigger the protection logic early.

Few things worth ruling out:

• Cell imbalance — even small differences (>20mV) can cause this at mid-SOC
• Charge current limit set in BMS config — easy to miss, there's a separate "charge overcurrent" setting that sometimes gets left low from factory
• Temperature sensor — if it's reading cold it can derate the charge rate

What's your actual cell voltage spread looking like right now? And which JBD model have you got? The older 4S units behaved differently to the newer ones with the Bluetooth dongle.

Also curious what you're charging from — if it's a Victron MPPT it could be the charger backing off rather than the BMS. Had a mate blame his JBD for weeks before realising his SmartSolar had been reprogrammed by accident.

Anyone else dealt with mid-SOC throttling on these? Be good to get a few more data points.

@TelScott75 makes a good point about cell lag — worth adding that JBD BMSs can also throttle if the charge voltage limits are set a bit conservatively from the factory. Had this exact thing on my cabin setup, pulled the settings up in Xiaoxiang BMS app and found the "charge overcurrent protection" was set lower than I'd expected. Bumped it up in line with what my cells were actually rated for and suddenly had full current back.

Also worth checking:

• Cable sizing between cells and BMS — voltage drop can confuse readings
• Temperature sensor placement (if fitted) — mine was reading cold air rather than actual cell temp
• Whether your Victron MPPT charge profile matches what JBD is expecting

The BMS is often just doing its job — question is whether it's working from accurate information.

Seen this exact thing on my shepherd's hut setup. Before diving into cell-level stuff, check your BMS discharge/charge temp sensors aren't reading funny — mine was throttling hard because a sensor had shifted and was giving a false low reading even on a mild day.

Also worth pulling the JBD app and looking at the actual cell delta. If it's under ~20mV you're probably fine and it's something else entirely.

What's your cable sizing like between cells and BMS? Had a mate with a Fogstar DIY build where undersized busbars were causing enough voltage drop to confuse the BMS into thinking it was closer to full than it was.

Good points all round, but one thing nobody's mentioned yet — check your inter-cell busbar connections. A high-resistance joint won't show up obviously until you're pushing current, at which point the BMS sees a voltage differential and backs off the charge rate to compensate.

Torque your busbars to spec (usually 4–6 Nm on M5 hardware), then do a proper IR test across each connection under load. I found a dodgy joint on my 280Ah Fogstar cells that was mimicking a weak cell almost perfectly — spent two days chasing BMS settings before I actually put a clamp meter on it.

Also worth connecting a laptop to the JBD via the Xiaoxiang app and watching cell voltages in real-time during charging. You'll see the lagging cell immediately rather than guessing from headline figures alone.

@RetiredSquaddie raises a good one on the busbars — caught me out on my boat bank last winter. I'd add: pull up the BMS app and check your cell delta during charging, not just at rest. If one cell is racing ahead voltage-wise while the others lag, the BMS will cap current well before full SOC to avoid tripping overvoltage on that outlier.

With JBD specifically, the default cell overvoltage threshold is often set quite conservatively from the factory — 3.65V on LFP isn't unusual, but if your cells aren't well-matched, one will hit that ceiling early and the whole bank suffers.

Worth logging a full charge cycle with the app open. Fogstar cells tend to be decently matched out of the box, but DIY builds with mixed cell batches are another story entirely.

@LazyNomad — the BMS log is a good shout. I'd also look at your charge source settings if you haven't already. If you're coming through a Victron MPPT, double-check the charge current limit in VictronConnect — it's easy to accidentally have it set lower than you think, especially if you've been playing around with profiles.

Also worth confirming your battery voltage settings match what JBD has configured internally. If the absorption voltage on the MPPT is set slightly below what the BMS expects, it'll just sit there looking like it's throttling when really it's already "done" from the controller's perspective. Caught me out last summer with my 280Ah bank.