Anyone else had issues with JK BMS dropping Bluetooth connection mid-charge?

Been running a 280Ah LiFePO4 pack (4x EVE 280K cells) in my campervan build for about six months now, paired with a JK BMS (the 200A active balancer version). Generally really happy with it, but I've noticed the Bluetooth drops out pretty consistently when the pack hits around 90% SOC during a bulk charge from my Victron MPPT. Reconnects fine a few minutes later, but it's annoying not being able to monitor it through the critical top-of-charge phase.

I'm using the JK app on Android (Samsung S21, so not an ancient phone). I've tried keeping the phone within a metre of the BMS, killed background apps, even factory reset the BMS once. Makes no difference. The BMS itself carries on doing its job fine — balancing kicks in properly, cell voltages all look good when it reconnects — so it's not a safety issue as such, just a monitoring headache.

Wondering if this is a known firmware quirk or whether the Bluetooth module just gets hammered when the active balancer is working hard and drawing more current? Has anyone flashed a newer firmware version and seen an improvement, or is this just one of those things you live with on the JK units? Happy to share my BMS settings if that helps anyone diagnose it.

Gazza24 | 847 posts | ⚡ Solar Addict

@Neil1978 yeah, had exactly this with my JK on a 16S LiFePO4 setup. Turned out the Bluetooth drops were heat-related — the BMS was mounted too close to my inverter and once temperatures crept up mid-charge, the connection would just vanish. Moved it to a better-ventilated spot and it's been rock solid since.

Worth also checking your phone's battery optimisation settings if you're on Android — Samsung especially will aggressively kill the JK app in the background and it looks like a BMS dropout when it's actually your phone being stingy with resources.

The JK app itself is a bit flaky too if I'm honest. Some lads on here swear by connecting via a Bluetooth-to-RS485 adapter and using a Raspberry Pi with MQTT instead. Bit of a faff but far more reliable.

DailyProject | 312 posts | 🔋 Off-Grid Enthusiast

@Neil1978 Worth checking if it's a power-related issue rather than the BMS itself. I found on mine that the Bluetooth module can get a bit flaky when the balancer is working hard and drawing more current — the internal voltage regulation on the BMS board gets a touch noisy. Try keeping your phone's screen on and Bluetooth active rather than letting it sleep mid-session, as the app sometimes struggles to reconnect after a timeout.

Also, make sure you're on the latest firmware — JK pushed an update a while back that specifically addressed connection stability. You'll need the PC tool via USB to flash it though, not the phone app. Bit of a faff but made a noticeable difference on my 8S setup. What firmware version are you currently running?

Nessa61 | 156 posts | 🔋 Off-Grid Enthusiast

@Neil1978 I had this exact problem last winter with my JK 150A unit. Turned out to be interference from my Victron MPPT kicking in at bulk charge — the BMS Bluetooth would drop almost every time. Fixed it by moving my phone closer and keeping other Bluetooth devices (particularly my stereo head unit) disconnected while monitoring. Also worth trying the JK app's "always connected" setting if you haven't already — there's a keep-alive option buried in the settings that made a real difference for me. Firmware version matters too; make sure you're on the latest via the app. What firmware are you currently running?

DailyWanderer | 203 posts | 🏕️ Cabin Dweller

Mine did the same in my static caravan setup until I realised the JK app just quietly sulks and disconnects if your phone screen locks — force-keep the screen on and suddenly it's magically reliable, which says more about the app than the BMS really.