How to find voltage data over the past 12 hours

Been down this rabbit hole myself recently, so thought it'd be worth opening it up for discussion here.

Running a Victron Cerbo GX in my van, I kept finding myself wanting to pull up battery voltage history — specifically across the night when I'm not awake to eyeball the BMV-712 display. You'd think it'd be obvious where to find it, but the VictronConnect app isn't actually where that data lives. Took me an embarrassing amount of time to realise you need to be looking at the VRM Portal instead.

Once you're in VRM, head to Advanced → Widgets, add a voltage graph, and you can dial in exactly the time window you want — past 12 hours, 24, whatever. It's all there, logged automatically as long as your Cerbo has either a data SIM or WiFi access. Mine pings through a Vodafone SIM on a basic data plan, costs next to nothing.

The VictronConnect app is more for real-time monitoring and device config — easy to conflate the two when you're starting out.

Where it gets interesting is interpreting what you find. I spotted a voltage sag around 3am during a cold snap last winter that I'd have completely missed otherwise — traced it back to the Fogstar Drift 200Ah cells not quite performing as expected in low temps. Adjusted my low-voltage cutoff settings as a result.

Curious whether anyone's found a slicker way to get quick-glance overnight graphs without digging through VRM every morning? And does anyone run local logging with something like Node-RED or a Raspberry Pi as an alternative? Would love to know what others have cobbled together.

@CoastalCamper interesting thread. On my motorhome setup I've been doing something similar with the Cerbo GX.

Quick question though — are you pulling this data via the VRM portal remotely, or are you accessing it locally through the Touch 50 display? I've found the VRM dashboard will give you historical voltage graphs going back well beyond 12 hours, but the resolution of the data points seems to vary depending on your logging interval settings.

Does anyone know what the minimum logging interval is on VRM before it starts averaging data rather than showing raw readings? I'm trying to work out whether voltage sag events during EV charging would actually be captured accurately, or whether short spikes/dips might get smoothed out before they're stored.

VRM portal's "Advanced" tab lets you plot voltage over custom time ranges — though naturally it only shows data from when your Cerbo decided it actually felt like connecting to the internet 📉

@CoastalCamper this is something I've been fussing over with my static caravan setup too. One thing nobody's mentioned yet — if you're not online consistently, it's worth checking your Cerbo's local data logging settings. It stores data on-device even without internet, and you can pull historical voltage readings via the local VRM dashboard (just hit the Cerbo's IP address on your network).

Also worth asking: what interval are you logging at? Default is every minute I think, but you can tighten that up if you want finer resolution during overnight discharge. Made a real difference when I was trying to work out whether my Fogstar 200Ah was actually hitting the low-voltage cutoff or if my BMS was just being twitchy.

What's your battery chemistry? That'd change what voltage thresholds you're actually watching for.

Great thread — this comes up a lot with tiny house builds too where you're trying to spot overnight sag patterns.

One thing worth flagging: if you're using a Raspberry Pi running Venus OS rather than a physical Cerbo GX, you get the same VRM logging but you can also SSH in and query the local database directly. Gives you a bit more flexibility if the VRM portal is playing up or you're off-grid with no internet connection at the time.

Also — does anyone know whether the data resolution changes depending on your VRM subscription tier? I've seen some forum posts suggesting free accounts downsample older data, which would obviously affect how useful those 12-hour plots actually are for diagnosing short voltage dips.