Anyone else had their Daly BMS randomly drop to 0% SOC mid-charge?

Picked up a 200Ah 12V LiFePO4 pack from a well-known eBay seller back in March, came with a 100A Daly BMS already wired in. It's been sitting in my van paired with a Victron MPPT 100/30 and generally behaved itself — until last week. Was sat at about 60% SOC, sunny day, panels pushing around 18A in, and the Daly app just suddenly showed 0% and the BMS cut the load. Came back on after about 30 seconds but it's happened three times since.

I've checked all the cell voltages via the app and they look balanced — sitting between 3.28V and 3.31V across all four cells when it drops out. No obvious overtemp either, it was only about 14°C in the van at the time. The only thing I can think of is that the current sensor in the Daly is throwing a wobble, because the SOC seemed to jump around a bit in the minutes before the cutoff.

Has anyone seen this on a Daly, particularly the Bluetooth app version? I'm wondering whether it's worth just resetting the SOC manually through the app and seeing if it settles, or whether this is a sign the BMS is on its way out. Also curious whether anyone's swapped a Daly for a JK BMS on a similar pack — looks like the JK might give more reliable coulomb counting but I don't want to rewire everything if there's a simpler fix.

Kelly1983 | 847 posts | ⚡ Solar Obsessive

@PanelRuss yes, had almost exactly this with my 150Ah pack last summer! Turned out the Daly's "battery capacity" parameter in the app was set completely wrong from the factory - mine was programmed for a totally different cell configuration. The BMS was losing track of SOC and essentially resetting itself when it got confused.

Download the Daly app (Android works better in my experience, iOS version is a bit flaky) and connect via Bluetooth if yours has that module. Check what capacity and cell count it actually thinks it's working with. Also worth checking your balance leads are all making solid contact - a dodgy connection can send it haywire mid-cycle.

What voltage is the pack actually sitting at when it drops to 0%? That'll tell us a lot about whether it's a comms issue or something more worrying.

GrumpySkipper | 1,204 posts | ⚡ Solar Obsessive

@PanelRuss Classic Daly behaviour, I'm afraid. The cheap ones are notorious for losing their SOC calibration, particularly when cell voltages drift apart even slightly. Your Victron MPPT won't be helping if absorption isn't hitting all cells equally.

Worth connecting the Daly to its PC software via the USB dongle (about £3 on AliExpress) and checking individual cell voltages during charge. I'd bet good money one cell is lagging and the BMS is panicking.

Also check your bulk/absorption voltage settings on the Victron - should be 14.2V and 14.6V respectively for LiFePO4. Running absorption too short means cells never properly balance.

Honestly though, if it keeps happening, a full capacity test followed by a proper top-balance of the cells individually is the only real fix. Pain in the backside but worth it.

OldSailor86 | 312 posts | ☀️ Off-Grid Enthusiast

Had this exact drama on my narrowboat two winters ago. The culprit for me turned out to be a loose balance lead on cell 3 — the BMS was reading phantom voltage spikes and throwing a wobble. Worth pulling the cover and checking each connection with a multimeter before you condemn the BMS entirely.

That said, @GrumpySkipper isn't wrong about the cheap Dalys. I eventually replaced mine with a JK BMS and the difference in reliability was night and day — proper Bluetooth monitoring too, so you can actually see what's happening inside the pack rather than guessing.

The Victron MPPT pairing shouldn't be causing this — mine runs the same combination without issue. Focus on the BMS and cell connections first.

LutonDream | 523 posts | ☀️ Off-Grid Enthusiast

@PanelRuss worth checking whether your Victron MPPT is set to lithium profile with the correct absorption/float voltages. If it's pushing above 14.6V even briefly, some Daly units will trip the overvoltage protection and reset their SOC counter to zero rather than gracefully cutting off. Seen it happen on a mate's setup in his Luton box van — identical symptoms to yours.

Also, are you communicating with the BMS via the Daly app over Bluetooth? The SOC calibration on these is notoriously drift-prone and sometimes a full discharge to low-voltage cutoff followed by a complete charge cycle will recalibrate it properly. Not a permanent fix necessarily, but worth ruling out before you start pulling connectors apart.

MuddyRanger | 89 posts | 🔋 Off-Grid Curious

@PanelRuss had almost identical with a Daly 100A in my shepherd's hut build last year. Turned out the BMS was losing its cell calibration after hitting an over-voltage protection event — basically it'd trip, recover, but the SOC counter had lost its reference point entirely.

Worth trying a full controlled discharge to near-empty, then a slow full charge to let it re-calibrate. Tedious but it sorted mine temporarily.

Long-term though I ditched the Daly and moved to a Fogstar-supplied pack with their own BMS — night and day difference in reliability. If you're staying with the Daly, JBD/JK replacements are a popular swap and talk properly via Bluetooth so you can actually see what's happening cell-level rather than guessing.

LesPhillips | 847 posts | ⚡ Off-Grid Veteran

I've got a Daly in my garden office build and saw this twice before I figured out what was going on. The culprit for me was the BMS losing its SOC calibration whenever a cell drifted out of balance — it essentially panics and resets to 0%.

Worth grabbing the Daly PC software (free download, just needs a USB-UART cable) and checking your cell voltages individually during charge. If one cell is consistently lagging the others by more than ~50mV you've found your problem.

@MuddyRanger — interesting you've seen it in a shepherd's hut too, makes me wonder if these cheaper Daly units just don't handle partial-state-of-charge cycling well long term.

A proper active balancer wired across the cells sorted mine permanently. About £15 off Amazon.