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

Picked up a JK BMS (the 200A, 4S LiFePO4 version) a few months back to go with my 280Ah cells from Amy at Alibaba. Generally really happy with it — balancing works a treat and the app gives you loads of useful data. But I keep losing the Bluetooth connection when the battery is pulling serious current, usually somewhere above 80A on the charge side. Happens on both my Android phone and my partner's iPhone, so it's not a handset thing.

I've tried keeping the phone closer, checked there's nothing obvious causing interference, and made sure I'm on the latest firmware (v11.25 if that means anything to anyone). It reconnects fine after a minute or two, but it's annoying when you're trying to keep an eye on cell voltages during a bulk charge from the alternator via a Victron Orion-Tr Smart 30A — though actually at 30A it seems fine, it's mainly when I'm also running my 400W of roof panels through a Renogy MPPT at the same time.

Has anyone cracked this, or is it just a known quirk of the JK? I've seen a few mentions of it on some Facebook groups but nothing concrete. Wondering if it's a power supply noise issue on the BMS board itself or just the Bluetooth antenna being a bit rubbish at high loads.

@WFS_Camper — had the exact same gremlin with mine on the shepherd's hut build last winter. Drove me absolutely mental until I realised it was a simple phone Bluetooth range issue combined with the BMS being tucked inside a metal enclosure.

Two things fixed it for me:

• Drilled a small vent hole near the BMS (needed for airflow anyway)
• Kept my phone within about 3 metres during bulk charge

The JK app also has a habit of dropping if your phone screen locks — worth going into your Android battery settings and disabling optimisation for the JK app specifically. Made a huge difference.

The BMS itself never actually stopped working, just lost the connection — easy to confuse the two when you're panicking at 2am watching your Victron MPPT do its thing! 😄

@WFS_Camper mine did this constantly in the van until I realised the BT module was just loose in the housing — a tiny wiggle and it'd drop out faster than my will to read another Victron manual.

@WFS_Camper worth checking whether it's specifically dropping during bulk charge phase — mine did exactly this and turned out to be interference from the alternator when driving. The BMS itself was fine, just the Bluetooth getting swamped.

Fixed it by moving my phone closer and making sure no inverter or charger cables were running parallel to the BMS wiring. Proper cable separation made a noticeable difference.

Also — have you updated the firmware recently? JK pushed an update a while back that apparently addressed some BT stability issues. You can flash it through the app itself if you're on Android. Might be worth trying before pulling the unit apart like @RiverFinn suggested, just to rule out a software gremlin first.

Been running the same unit for about eight months now and had similar bother early on. One thing nobody's mentioned yet — check your phone's Bluetooth settings and make sure battery optimisation is disabled for the JK app. Android especially will aggressively kill background connections to save power, and it looks like the BMS is dropping when actually it's your phone booting the app out. Made a massive difference for me once I sorted that. Also worth making sure you're on the latest firmware — JK pushed an update a while back that apparently addressed some BT stability issues. You can flash it through the app itself if you haven't already. @TransitNomad's point about the bulk charge phase is interesting though, that does sound like a separate hardware thing worth digging into.