Anyone else's Victron Cerbo GX randomly deciding it's 1970 after a leisure battery swap?

Pulled out my old AGM and dropped in a shiny new Fogstar Drift 100Ah LiFePO4 yesterday — lovely bit of kit, no complaints there — but now my Cerbo thinks it's the 1st of January 1970 every time I kill the van's ignition. Timestamps on my VRM logs look like I'm filing data from before the moon landing.

Tried the obvious stuff: checked the RTC battery on the unit, reflashed the firmware (v3.40), even gave it a stern look. Still reverts to Unix epoch zero the moment shore power and the leisure bank both drop out simultaneously.

Running a Renogy 175W panel on the roof — wondering if there's some minimum voltage threshold the Cerbo needs to maintain its clock that I'm somehow just missing with winter sun in the Scottish Borders. Anyone had this and actually fixed it, or is this just van life now?

@FellGraham had exactly this with my static setup after a battery swap. The Cerbo loses its RTC when power's completely cut — 1970 is just Unix epoch zero, so it's basically throwing its hands up.

Fix is straightforward:

• Connect it to VRM (via WiFi or dongle) and it'll sync NTP automatically
• If you're off-grid with no internet, you can manually set it under Settings → General → Date & Time in the VRM local interface

Worth also checking your battery profile has been updated for the LiFePO4 chemistry — AGM settings left in place can cause all sorts of odd behaviour beyond just the clock.

The Fogstar Drift is a cracking battery by the way, running one myself. Just needs the charge parameters dialling in properly.

Cerbo_Fan replied:

@FellGraham Classic Unix epoch reset! The Cerbo loses its RTC when power drops completely during the swap — LiFePO4 batteries often have a slight delay before the BMS closes the circuit, which is just long enough to wipe it.

Two things worth trying: first, connect it to your phone hotspot via Bluetooth and let VRM sync the time automatically over the internet. Takes about 30 seconds. Second, if you're not running VRM, you can set the time manually under Settings > General > Date & Time on the touchscreen.

Going forward, a small 9V backup battery wired across the input before you disconnect your main leisure battery prevents this entirely. Some folks keep a little USB power bank plugged into the GX Touch during swaps for the same reason.

Shouldn't cause any lasting issues though — just an annoyance! 👍

Gill1990 replied:

@FellGraham Yep, seen this a fair few times! Worth knowing the quickest fix is just making sure your Cerbo has an active internet connection via WiFi or ethernet — it'll pull the correct time automatically via NTP and sort itself out within a minute or two. If you're often off-grid without a connection, a cheap GPS dongle plugged into the USB port works an absolute treat as a time source. Victron's VRM portal also helps keep things synced when you do get signal. Going forward, if you can avoid completely isolating the Cerbo during battery swaps (even a small 12v power bank on the input temporarily) it'll hold its RTC settings. Dead handy to know about before your next swap! 👍

MoorDweller replied:

@FellGraham The others have covered the RTC side well, but worth mentioning that once you've got time sorted, double-check your battery settings in the Cerbo too. Swapping from AGM to LiFePO4 means your charge profile will be completely wrong out of the box — absorption voltage, float voltage, the lot. The Fogstar Drift wants roughly 14.2–14.6V absorption and around 13.5V float, quite different from what your AGM was running on.

If you're on VRM portal, the Cerbo should pull the correct time from the internet automatically once it gets a connection. No internet on site? A cheap GPS dongle plugged into the USB port sorts the time sync permanently without needing WiFi. Worth the few quid if you're often off-grid. I've had mine running solid for two years that way.

My Cerbo did the same thing when I rewired my garden office setup — just enable NTP sync in the Remote Console under Settings > General and it'll pull the correct time the moment it sniffs a WiFi signal, never looked back. 📡

Squib82 replied:

Worth adding one thing nobody's mentioned yet — if your Cerbo is off-grid without a consistent internet connection (as mine is on the boat), NTP sync won't always save you reliably. The RTC capacitor on older Cerbo units does degrade, so after a full power loss it genuinely cannot hold time.

Check your firmware version first; Victron quietly improved RTC handling in some VenusOS releases. If you're still seeing drift, a GPS dongle plugged into the Cerbo's USB port gives it a hardware time source completely independent of connectivity — works a treat and costs almost nothing.

Also double-check your battery settings profile after the AGM-to-LiFePO4 swap. The timestamp issue sometimes masks the fact that charge parameters haven't been updated to suit the Fogstar's chemistry, which is arguably the more pressing problem anyway.

Your Cerbo just lived through the entire disco era, punk, Thatcher, the Spice Girls, and Brexit in about 30 seconds — respect the commitment to historical accuracy, honestly.

But yeah, LiFePO4 cells don't hold a trickle the same way AGMs do, so your RTC loses its mind the moment power drops. If you're regularly off-grid like me and NTP isn't an option, a cheap USB GPS module feeding time sync via VRM does the job — bit faffy to set up but solid once it's running.