How do you interpret long-term battery behaviour in VRM?

Been running my Victron setup on the static van for about 3 years now and honestly VRM is both a blessing and a curse — drowning in graphs but still not entirely sure what I'm supposed to be panicking about. 😅

My Fogstar Drift LiFePO4s look "fine" on paper but I've noticed the resting voltage after a full charge has crept down ever so slightly over the past 18 months. Probably nothing, probably everything, who knows.

A few things I've started actually paying attention to rather than just vibing at the dashboard:

• Charge acceptance rate — are the cells hitting absorption quicker than they used to?
• SoC drift vs actual voltage — when Victron's SoC estimate starts lying to you noticeably, something's shifting
• Temperature correlation — my van's uninsulated so winter capacity dips are real, but I track whether summer performance is recovering to where it was the year before

The EV charging side of my setup (yes, I charge a Leaf off solar 😬) makes the discharge curves look absolutely mental so that doesn't help interpretation.

What I genuinely can't work out is whether VRM's long-term trend data is actually useful for spotting gradual capacity fade, or whether you need to do a proper manual discharge test every year to get real numbers.

Anyone else with a few years of VRM history — do you have a rhythm for reviewing it, or do you just wait until something goes wrong like the rest of us? Particularly curious if anyone's running Pylontech or similar racked batteries and whether the BMS comms data tells a cleaner story than DIY setups.

@BorderVanLifer the metric I keep coming back to is the discharged energy trend over rolling 30-day periods. If your usable capacity is silently shrinking, that's where it shows first — same solar input, same loads, but the bank hits absorption earlier and earlier.

Also worth pulling the battery voltage vs SOC scatter — if it's tightening into a weird curve or showing splits between charge/discharge traces, your cells are drifting and your BMS calibration is probably lying to you about state of charge.

Three years in you're likely seeing genuine degradation starting, not just noise. I noticed on my Fogstar Drift cells around month 28 that minimum night voltage crept up by about 0.3V without any load change — subtle but it was the earliest warning sign before anything obvious showed up.

@BorderVanLifer three years of VRM data and you're still not panicking? Honestly that is the metric — panic onset latency 😄

Seriously though, the thing I watch that nobody mentions: State of Health drift vs seasonal temperature correlation. My Fogstar Drift cells looked absolutely terrible last February and I nearly ordered replacements.

@MoorLee that got a laugh but it's not entirely wrong — three years without incident on a static install probably means either the setup is solid or the problems are slow enough that you haven't clocked them yet.

What I actually watch on mine is the minimum daily voltage under load rather than SoC percentages. BMS-reported SoC drifts over time and I don't trust it blindly. But if that voltage floor is creeping down month-on-month at equivalent load conditions, something's changing in the cells.

Also worth pulling the battery temperature logs if you're not already — capacity quietly degrades faster in cold than most people expect, and a static van in a Welsh winter will tell a different story to summer figures. Comparing same-season data year-on-year is more honest than raw averages.

@BorderVanLifer one thing I'd add to what @VanRhys was getting at — look at your absorption time trends over the same rolling periods. As lithium ages (or if you've got a sneaky cell going rogue) you'll often see absorption either getting suspiciously shorter or the MPPT working harder to hit the same float voltage. Neither on its own is a red flag, but if you cross-reference that against your minimum daily SOC over winter months, patterns start emerging that raw capacity figures can mask. Three years of clean data is genuinely useful baseline material — most people don't have that luxury. @ExBrickie is right that no drama probably means you've done something right, but it's worth setting up a simple spreadsheet pulling those monthly averages before the data becomes so normal you stop noticing the slow drift.

@WezBrown66 makes a solid point on absorption time — I'd also keep an eye on your State of Health trend in VRM if you're running a Victron-compatible BMS. On my static caravan setup I noticed SoH creeping down faster than expected and it flagged a cell imbalance issue before anything dramatic happened.

The other thing worth watching is minimum daily voltage under load across the same season year-on-year. If you're hitting the same trough voltage noticeably earlier in the day compared to previous summers, your usable capacity is shrinking even if the headline numbers look fine.

Three years is actually a decent dataset — export the CSV and plot absorption duration against ambient temperature. Strips out the seasonal noise and shows you the actual degradation curve rather than just reacting to whatever VRM throws up on screen.