Anyone else had grief with their JK BMS dropping Bluetooth mid-charge?

Been running a 280Ah LiFePO4 pack in my van build for about six months now — four EVE 280K cells wired in 4S with a JK BMS (the 200A active balancer version). Overall I'm well happy with it, but I've started noticing the Bluetooth connection to the JK app just dies randomly, usually somewhere between 80–90% SOC when the cells are under load from my 40A DC-DC charger. Have to kill the app and reopen it two or three times before it picks back up. Doesn't seem to affect the BMS operation itself, just the monitoring side.

I'm running the app on Android 13, and the BMS firmware is on the older side — V11.25 I think. Wondering if it's a firmware thing, an Android compatibility issue, or just the JK Bluetooth being a bit pants in general. Seen a few vague mentions of it on Facebook groups but nothing concrete.

Has anyone actually updated the JK firmware over Bluetooth and is it straightforward, or is there a chance of bricking the thing? Bit nervous about flashing anything on kit that's sitting in the middle of my battery management setup. Any experience or advice would be dead useful.

PanelTina | ⚡ Solar Obsessive | Posts: 847

@ExSquaddie97 Yes! Drove me absolutely mad for weeks before I figured it out. Mine was dropping Bluetooth every time the balancer kicked in at higher charge voltages — turned out to be interference from the active balancing circuit itself.

Two things that helped me: first, make sure your phone's Bluetooth isn't set to low-power mode, as the JK app struggles to maintain connection when the signal gets even slightly noisy. Second, and more importantly, try repositioning your phone closer to the BMS during charging — the antenna on these units isn't brilliant.

Some folk on here have also had success updating the BMS firmware through the app when connected via USB instead. Worth checking you're on the latest version either way.

What's your cell voltage sitting at when it drops? That might help narrow it down.