My BMZ battery is on idle won't wake up

So I've run into a strange one and wondering if anyone's seen this before.

Been running my shepherd's hut setup for about 8 months now — 24V BMZ battery bank paired with a Victron Multiplus. Everything's been solid until a couple of nights ago.

I'd set up a scheduled load (running a small workshop heater overnight on a timer) and when I came out in the morning the whole system had gone into some kind of sleep/idle state. The BMZ BMS is showing the idle indicator and it just won't wake back up. No response to load demand, no response to pressing the wake button on the unit.

Few things I've tried already:

• Disconnected all loads and the Victron entirely
• Left it 20 minutes and reconnected
• Checked all DC connections (all tight, no corrosion)
• Pulled up VictronConnect logs — it shows the battery comms dropping off around 2am

My suspicion is the BMS went into a protection mode when the load kicked in — possibly a voltage dip triggered something — but I genuinely don't know how to force a proper wake cycle on the BMZ without risking doing something daft.

Does the BMZ need a specific charge voltage applied to wake it from idle? Or is there a manual reset procedure I'm missing? I've had a hunt through the documentation that came with it and it's frankly useless.

Anyone run BMZ batteries off-grid (rather than in a typical home ESS setup) who's dealt with this? Curious whether it behaves differently without grid as a reference point.

@BatteryWez classic BMZ "deep sleep" drama — you'll need to tickle it awake with a small external charge source (even a cheap bench PSU will do) to get the cell voltage above the BMS wake threshold, because the Multiplus won't see it as a valid battery and will just sit there blinking at you like a confused labrador.

@48VQueen has the right idea — the "tickle" method is indeed the technical term (probably).

Worth knowing: BMZ's sleep threshold can be aggressively conservative. Mine on the boat did the same after a gloomy January fortnight — basically sulked harder than a teenager who's lost their Xbox.

A bench power supply set just above your

@48VQueen and @BrianBrown have covered the wake-up side, but worth flagging — once you do get it back online, dig into why it went that deep in the first place.

On my boat setup I had similar with a different BMS and it turned out the Multiplus absorption settings were letting the bank drift lower than it should between charge cycles. Tweaked the float voltage and haven't had the issue since.

Check your Victron logs if you've got a Cerbo or CCGX — they'll show you exactly where the voltage bottomed out. If it's happening repeatedly, the battery's going to hate you for it long-term. BMZ cells aren't cheap to replace.

Might also be worth a call to wherever you bought it — some BMZ units still have warranty support and they're occasionally helpful about this stuff.

@ExBrickie raises the critical point — and to add a pedantic but important layer: before you tickle it awake, check the BMZ BMS communication port is actually connected to your Multiplus via the VE.Bus or CAN interface.

Nine times out of ten these "mystery sleep" events are the BMS and inverter having a domestic because they've lost their chat — the battery trips to protect itself and then can't receive the wake signal through the proper channel.

Pull the comms cable, reseat it, then attempt the tickle charge. Your Victron CCGX or Cerbo (if you have one) should show the battery state clearly once comms are restored — if it's still showing "unknown" after wake-up, you've got a separate wiring gremlin to hunt down.