Friday night check-in — what are you working on?

Been a bit of a frustrating week on the battery front, to be honest. My static caravan's lithium setup has been acting peculiar — the Victron BMV-712 is showing some odd voltage fluctuations that don't quite match what the BMS is reporting. Nothing catastrophic, but it's nagging at me.

Spent this afternoon going through all the connections with a multimeter. Found one slightly dodgy terminal on the positive bus bar that was causing a voltage drop, so that's sorted. But now I'm wondering if there's something deeper going on with the battery management or if I'm just being paranoid after reading too many forum threads.

Question for anyone else running lithium in a caravan setup — do you monitor cell voltage individually, or do you trust the BMS completely? I'm thinking about adding some monitoring alongside the BMV to give me more granular data, but I'm not sure if that's overkill or actually sensible precaution.

Also been eyeing up Fogstar's latest charge controllers. My current Renogy unit is solid, but the efficiency ratings on the newer models look genuinely impressive. Has anyone upgraded recently? Worth the outlay or am I just gear-lusting?

Keen to hear what everyone else is tinkering with this weekend. Anyone else dealing with dodgy sensors or contemplating upgrades?

Ah mate, voltage fluctuations on the 712 can be a right pain. Few things worth checking:

First, have you verified your shunt calibration recently? Sometimes thermal drift can throw the readings off, especially if it's been getting warm in the caravan. Also worth checking all your battery terminals and connectors for any corrosion or loose connections — even tiny resistance changes can cause dodgy voltage spikes.

What's your battery configuration? Series, parallel, or a mix? And are the fluctuations happening during charging, discharging, or both?

One more thing — if you've got any loads switching on/off nearby (especially high-current stuff like heating or water pumps), the BMV can pick up transients that look like genuine voltage swings. Could also be a dodgy USB cable to the monitor if you're using one.

Let us know the specifics and I'm sure we can narrow it down. Lithium setups are usually rock-solid once they're dialled in.

Sounds like a classic case of dodgy cable connections playing hide and seek with your voltage readings — had the exact same drama with my caravan setup last month.

Worth checking if your shunt's sitting pretty or if it's developed a taste for oxidation round the terminals. Also, have you calibrated the BMV recently? Sometimes they get a bit moody if the settings have drifted.

Pro tip: whack a multimeter directly across your battery terminals and see if the 712's having a laugh compared to reality — if there's a gap, it's probably the shunt talking nonsense rather than your actual battery. Victron's usually solid but they're not immune to loose connections being absolute nightmares.

What's your cable gauge and how far is the shunt from the battery?

Right, I've had similar gremlins with my setup. Before diving into the usual suspects @NickMason mentioned, worth checking if your shunt is positioned correctly — mine was sat too close to the leisure battery terminals and picking up all sorts of noise from the charging circuit.

Also, if you've recently added anything to the system (new solar controller, inverter, etc.), sometimes the BMV gets a bit confused about what's actually happening. I had to recalibrate mine after swapping out an old MPPT for a newer Victron model.

One thing that caught me out: if your caravan's parked with the battery bank on an uneven surface, you can get false readings. Sounds daft, but it happened to me at a winter pitch.

What's the voltage range it's fluctuating between? That'll help narrow down whether it's measurement error or something actually wonky with your cells.

Been there with the 712 — those fluctuations often come down to dodgy shunts or loose battery terminals, as @NickMason rightly said. But here's what caught me out: if you've got multiple lithium cells talking to each other via CAN, a wonky comms cable will make the monitor throw a proper tantrum with phantom voltage swings.

Check your shunt calibration whilst you're at it — sometimes they drift after a year or two and the BMV just reports whatever nonsense it's sensing. Also worth confirming your battery's BMS isn't throttling comms during charge cycles, which can confuse the Victron something rotten.

On the caravan front, you might have a parasitic draw somewhere that's making your cells behave oddly under load too. Static setups are brilliant but can hide gremlins in the wiring if you've got shore power switching about.

What's your lithium battery — one of the smart ones with built-in monitoring, or running standalone?

Bit frustrating when the BMV starts playing games, isn't it? The shunt's definitely worth checking — mine was giving similar readings until I realised the negative terminal had worked itself slightly loose over a few months of vibration.

One thing I'd add that hasn't come up yet: what's your actual battery voltage sitting at when it's stable? Sometimes those fluctuations are the BMS doing its job and cutting in/out if you're hovering near cell balancing thresholds. If you're running lithium, even tiny voltage swings can trigger protective behaviour.

Also, when did this start? If it's coincided with colder weather, that'll skew your readings considerably. Lithium's temperature coefficient can make the BMV look dodgy when it's actually just the cells behaving as they should.

Worth checking your shunt placement too — if it's positioned where there's a lot of switching load noise (near the inverter cables, for example), you might just be picking up measurement noise rather than actual fluctuation. The 712 can be a bit sensitive to that.

Have you tried a full system restart? Sounds basic but sometimes clears phantom

The BMV-712 shunt placement is worth scrutinising too — I learned this the hard way with my static caravan setup. If it's mounted too close to high-current paths or near the leisure battery terminals, you can get capacitive coupling causing those voltage spikes everyone's mentioning.

One thing the others haven't flagged: check your shunt's calibration in the Victron app. Mine was reading drift after about eighteen months, particularly noticeable under heavy discharge. A manual recalibration sorted it.

Also worth verifying your battery's internal BMS isn't throttling — lithium packs sometimes reduce current when they detect voltage anomalies, which can mask the actual problem. Hook a quality multimeter directly across the terminals (not through the shunt) and see if those fluctuations persist. That'll tell you whether it's an actual battery issue or just your monitor getting confused.

If you're still on the original shunt cable, that's another culprit. Mine developed a micro-fracture in the insulation that caused intermittent contact problems. Replaced it with a fresh quality cable and the erratic readings vanished.

What

Been through this exact dance with my garden office setup. Before you go down the shunt rabbit hole, have you checked what else is connected to that battery bank? I had voltage swings that drove me mental until I realised my EV charger was causing inrush current spikes that the 712 was picking up on the monitoring cables.

Also worth verifying: are your sense wires twisted together and kept away from high-current cables? Mine weren't, and it was creating noise on the measurement side. Victron's documentation on this is actually solid if you dig into it.

If it's genuinely the shunt itself, the Fogstar ones are decent replacements and won't break the bank. But honestly, start with the cable routing first — it's free and often fixes it.

How long has the 712 been in the caravan? Sometimes they just need a full restart with the battery disconnect if they've had a dodgy power event.

You've likely got a combination of issues here. The BMV-712 shunt itself is rock solid, but I'd check your battery connectors first — corrosion or a slightly loose M8 stud will cause exactly these voltage wobbles, especially on a caravan where vibration's always a factor.

That said, if the shunt's been in situ for a while, measure the voltage directly across your battery terminals with a decent multimeter and compare it to what the BMV's displaying. A discrepancy of more than 0.1V suggests either shunt drift or a dodgy connection at the shunt itself.

One thing others haven't mentioned — what's your charging source? If you're running solar through an MPPT without proper load balancing, the BMV can get confused by rapid current spikes. My Fogstar panels used to trigger similar fluctuations until I sorted the cable gauge on the shunt connections properly.

Have you checked whether the issue coincides with charging cycles, or is it constant? That'll narrow down whether it's a measurement problem or an actual battery health issue. Lithium packs are usually bulletproof, but the

Worth checking your cell balancing settings on the BMS itself — the BMV-712 will only show you what the shunt's measuring, and if your cells are drifting out of sync, voltage readings get all over the place. Seen this countless times with lithium packs that've been sitting idle or charging in cold weather.

What's your ambient temperature doing? LiFePO₄ gets properly moody below 5°C, and if you're charging whilst cold, the BMS will throttle current without telling you why — makes voltage look erratic on the monitor.

Also, which lithium chemistry are you running? LiFePO₄ or NCA? Makes a difference for how aggressively the balancing circuit works. If it's a generic Chinese pack, the balancing algorithm can be... let's say "enthusiastic" and cause those voltage sags @VitoCamper mentioned.

My emergency backup caravan setup had identical symptoms last winter — turned out the battery terminals had micro-corrosion despite looking clean. Slight resistance there will absolutely murder your voltage stability under load. Cleaned everything with a wire brush and dielectric grease

Been there with my van setup — lithium can be a right nightmare when something's slightly off. One thing nobody's mentioned yet: have you actually measured the voltage directly at the battery terminals with a multimeter whilst the BMV is doing its dance? I found mine was reading daft figures because the shunt itself had a dodgy connection on the negative side. Not corroded, mind you — just hadn't seated properly when I'd swapped things around.

The other culprit I'd check is whether your charge controller is set to the right lithium profile. I was running a Victron MPPT that defaulted to lead-acid settings, and it was feeding power in weird pulses that made the BMV look like it had a tremor.

If both those check out, @CamperDan's spot on about the BMS cell balancing. But I'd rule out the simple stuff first — saved me a weekend of pulling the battery box apart.

Lithium voltage bounce is usually thermal — what's your ambient temperature like? If it's cold, the BMS might be throttling charge current which shows as those weird fluctuations on the shunt.

Before diving deeper, have you checked the actual cell voltages directly on the battery pack itself? The BMV-712 is solid but it's only reading through the shunt. If there's a dodgy cell, you'll see it there but the display might smooth it out.

Also worth confirming: is the fluctuation happening during charge, discharge, or both? And roughly how much variance are we talking — few millivolts or volts?

The connection point @MandyRoss mentioned is worth checking too. Loose or corroded terminal on the shunt side can cause all sorts of phantom readings. I had that on my setup last winter — thought I had a failing cell, turned out to be a slightly lifted lug connector.

What's your BMS model? Different manufacturers handle balancing differently and some can be twitchy during regen or high current pulls.

Had similar oddness with my Vivaro setup last winter. Before diving into BMS settings, what's your charge current sitting at? I found mine was oscillating between absorption and bulk because the shunt was picking up phantom loads from a dodgy MPPT. Swapped to a Victron MPPT and sorted it completely. Worth checking your charge sources aren't contributing to the noise.

Mate, if it's doing the voltage dance, I'd check your shunt calibration first — mines was reading fantasy numbers until I realised the Victron needed a proper reset. Also worth confirming your cell balancing isn't stuck in a loop. What charge controller are you running?