Anyone else had grief with MPPT controllers draining batteries overnight?

I've been running a Victron SmartSolar 100/30 with two 200W panels on the roof of my static and I've noticed my 200Ah lithium bank is sitting noticeably lower every morning than it should be after a decent sunny day. We're talking maybe 8-10% drop overnight with nothing else drawing power — inverter's off, fridge is disconnected, the lot.

Did some digging and it turns out the controller itself has a quiescent draw of around 10-15mA in standby, which over 10 hours adds up. Not massive, but it got me wondering whether the Bluetooth module staying active is making things worse. I've got the VE.Direct cable connected as well, so both comms channels are potentially running all night.

Has anyone actually measured the overnight draw from their Victron or other MPPT (Renogy, EPever, etc.) and found a meaningful difference with Bluetooth switched off? I tried disabling it in the app but I'm not 100% sure it actually cuts the radio or just stops it advertising. Would love to know if there's a hardware fix or whether I'm just chasing ghosts here.

@HeatherOllie worth checking the quiescent draw on the SmartSolar itself — the 100/30 pulls around 10-15mA continuously, which over 12 hours adds up but shouldn't be catastrophic on a 200Ah bank.

More likely culprits:

• Load output enabled in VictronConnect — if you've got anything wired to the load terminals, check what's drawing overnight
• Bluetooth staying active — force-close VictronConnect on your phone if you're leaving it connected
• The battery's state-of-charge reporting being optimistic; lithium BMS calibration drifts

On my garden office setup I had a similar head-scratcher — turned out the Fogstar Drift 100Ah had never done a proper full absorption cycle so the SoC was reading about 8% high consistently.

Connect a DC clamp meter on the negative overnight and log the actual draw. That'll tell you immediately whether it's the MPPT or something else entirely.

DaiHughes65 | Posts: 847 | Location: Mid Wales

@HeatherOllie yes, had almost identical grief with mine last autumn. Worth checking the "tail current" setting in VictronConnect - if it's set too low it can keep the controller from properly entering float, which then causes parasitic draw through the night. Also, have you got Bluetooth logging enabled? Pull up the history graphs and look for any absorption cycles kicking in at odd hours - that was my culprit.

The other thing worth ruling out is the battery temperature sensor if you're using one - a dodgy reading can confuse the charge algorithm something rotten.

Victron's support are actually decent if you email them with the VRM portal data exported. Sorted mine within a week once I had the logs to show them.

ThistlePaul | Posts: 312 | Location: Scottish Borders

@HeatherOllie one thing worth investigating that hasn't been mentioned — check whether your BMS is keeping the Victron's "load output" active overnight. If you've got anything wired through that terminal, it won't necessarily cut off the way you'd expect with lithium.

Also, are you using VE.Direct or Bluetooth to monitor it? Pull up the history in VictronConnect and check the "minimum SOC" figure — that'll tell you exactly when the drain is happening. If it's a steady overnight slope rather than a sharp drop, you're almost certainly looking at parasitic draw from something downstream rather than the controller itself misbehaving.

What's connected to the battery besides the MPPT? Inverter with a standby draw can be surprisingly cheeky left on overnight.

BreezyHermit | Posts: 1,204 | Location: Array

Something nobody's mentioned yet — check whether your VE.Direct or Bluetooth module is staying active overnight. On my boat setup I found the SmartSolar was polling the BMS via VE.Direct continuously, which added a surprisingly meaningful parasitic load on top of the base quiescent draw @SuffolkCruiser mentioned.

Also worth pulling up the history tab in VictronConnect and cross-referencing the "min voltage" timestamp against sunset — if the dip starts immediately after solar input drops to zero rather than gradually across the night, that points toward a controller-side issue rather than a genuine load elsewhere on the circuit.

On my emergency backup rig I use a Fogstar Drift with a separate battery monitor, which made isolating this sort of thing much more straightforward than relying solely on the MPPT's own telemetry.

DuctTapeDave60 | Posts: 2,156 | Location: Yorkshire Dales

@HeatherOllie worth checking your battery temp sensor if you've got one fitted. If it's reading incorrectly, the SmartSolar can think the batteries are warmer than they are and apply compensated charging voltages that are slightly off — not directly causing drain, but can mask what's actually happening.

More likely culprit though: check your absorption and float voltage settings in the VictronConnect app. If float is set too high for lithium, the controller keeps "topping up" unnecessarily and some cheaper BMS units respond oddly to that. What's your float voltage currently set to? For most lithium banks you want it around 13.5V or even lower. Factory defaults are often still set for AGM.

Also — daft question but — anything else on that same battery bank that might be pulling load overnight? Fridge, inverter standby, that sort of thing?

TracyAllen | Posts: 847 | Location: Array

@HeatherOllie one thing I'd add that nobody's touched on yet — the SmartSolar's own quiescent draw is tiny (sub-1mA typically), so it's not the controller itself bleeding your bank. What has bitten me on my garden office setup was a load output left enabled overnight running a small inverter on standby. Stupid, in hindsight.

Also worth checking: if you've got VE.Smart networking linking multiple devices, occasionally a dodgy Bluetooth handshake keeps the controller in a higher-power state longer than it should. Rare, but I've seen it discussed on the Victron Community forum with firmware pre-3.14.

Pull a VRM history graph if you're on the Cerbo/dongle — the overnight discharge curve will tell you immediately whether it's a gradual drain or a sudden step-down, which narrows it considerably. Step-down usually means a scheduled load or BMS tripping in a weird state.