Smart BatteryProtect 48V-10A — Alarm output inactive on startup when voltage already below threshold

Has anyone else noticed this with their Smart BatteryProtect setups?

Been running a 48V system in my shepherd's hut for about eighteen months now, and I've just started digging into the alarm outputs properly. Got a Victron Smart BatteryProtect 48V-10A controlling the main loads, and I'm trying to wire up proper low-voltage warnings.

Here's what's puzzling me: if I power everything up when the battery's already below the alarm threshold, the alarm output doesn't seem to trigger. But if the voltage drops into that threshold during normal operation, it fires up no problem. It's like the device only recognises the transition, not the state itself.

Is this just how Victron's programmed it, or have I got something misconfigured? I'm using the default settings at the moment—16V alarm point on a nominal 48V bank. Obviously if you're starting with a flat battery, you'd want to know about it straightaway rather than waiting for it to drop further.

Currently I've got the alarm wired to a simple relay that triggers a buzzer and cuts non-essential loads. Works great for the transition catching, but I'm wondering if I should add a separate low-voltage monitor just as a belt-and-braces safety net.

Keen to hear how others have set theirs up, especially anyone managing multiple battery banks or more complex systems. Does the VRM app show anything different, or is this a hardware limitation?

I've got a Smart BatteryProtect on my cabin setup and noticed similar quirks with the alarm logic. The device doesn't trigger the alarm output if the voltage is already below threshold when it powers up — it's looking for a crossing event rather than a static low voltage condition.

Worth checking your VRM settings and the actual alarm configuration in Victron Connect. Sometimes the alarm delay settings can mask what's happening too.

What voltage threshold are you running? Might be worth a quick email to Victron support with your system config — they're usually helpful with these edge cases. In the meantime, you could layer in a separate low-voltage monitor if the alarm output is critical for your setup.

Have you checked whether the alarm is configured to trigger on voltage drop rather than absolute voltage? The Smart BatteryProtect can be a bit finicky about this depending on your VRM settings.

I'm running a similar 48V setup in my static caravan and had the same issue — the alarm wouldn't fire on startup if the battery was already sitting below the threshold. Turns out mine was set to only alarm on a change in state, not a continuous condition.

Worth checking your Victron Connect app settings. Also, what's your actual voltage sitting at on startup? If it's dropping quickly during load, the threshold timing might be catching it mid-drop rather than triggering at rest.

Are you using this for low-voltage disconnect on your EV charger or general system monitoring?

I'd check whether you've got the alarm configured to trigger on a drop versus an absolute threshold. Mine took me ages to figure out — the Smart BatteryProtect logic can be a bit counterintuitive on first look.

That said, there's also a potential firmware quirk where the alarm output won't activate on startup if the voltage is already below threshold when you power up. It's more of an edge case, but I've seen it reported on the Victron community forums. Worth checking if you're running the latest firmware version — there were a few improvements in the 4.xx releases around alarm behaviour.

@Bazza, what's your current firmware version? Also worth confirming whether your alarm is set to latch mode or momentary — makes a real difference in how it behaves across power cycles.

Mate, mine does exactly the same — alarm sits silent until it drops below the threshold, not when it's already sitting there like a sad battery. Drove me round the twist for weeks.

The Smart BatteryProtect logic is: "Has voltage crossed the line?" not "Are we currently below it?" So if you're already parked up with a dodgy battery sat at 47V when you power on, the alarm thinks everything's fine until you dip to 46V.

Worth checking your alarm type setting in VictronConnect — mine needed switching from "relay" to "voltage drop monitor" or similar (can't remember the exact wording). If that doesn't sort it, might be worth a support ticket to Victron; they're usually spot on with firmware quirks.

Yep, classic Victron gotcha that one — the alarm logic only fires on the transition, not the state. So if your batteries wake up already knackered, the BatteryProtect thinks "nothing to report, mate."

Workaround: manually trigger a brief disconnect/reconnect cycle to reset the logic, or bang the threshold slightly higher than your actual floor voltage so it catches the drop. Bit clunky but beats wondering why your alarm's having a kip when your system's gasping.

On my boat I just learned to live with it and check the VRM dashboard instead — Victron's philosophy seems to be "alarms are for changes, not conditions."

@VickyWard nailed it, but worth adding — you can bodge around this by wiring a cheap normally-closed relay off the alarm output and setting your monitoring to check relay state on boot rather than waiting for the edge trigger, saved my shepherd's hut fridge from a very sad morning last February. 🐑🔋

@BatteryPaula that relay trick is decent but adds another failure point tbh. What I did on my static caravan setup was just wire the SmartShunt's relay output in parallel — it holds state properly regardless of startup conditions. Victron's own ecosystem sorts it out if you use the right bits together. The BatteryProtect alarm was never really designed to be a primary warning system anyway, more of a last-ditch cutoff signal. Might be worth checking your VictronConnect app too — you can set up notifications there that are state-based rather than transition-based.