Anyone else running a 200W solar setup in their van? Battery drains overnight

I've got a similar setup and I'm seeing the same issue. 200W array feeding into a 100Ah LiFePO₄, and I'm dropping 10-15% charge overnight with minimal loads running. Getting rather frustrating.

Before we assume it's parasitic drain, have a few questions that might help us both troubleshoot:

What's your actual load profile? I initially thought my problem was the battery, but realised my fridge was pulling far more than anticipated—even in eco mode. Are you monitoring individual circuits?

Is your BMS cutting the battery off at night? I had my Victron configured to protect the battery below 20%, which meant phantom loads were discharging it further. Worth checking your settings.

Solar input during twilight hours? 200W doesn't sound like much when you factor in low winter angles and panel orientation. What's your average generation on a proper sunny day? I found my expectations were wildly optimistic until I actually logged real figures.

The worrying bit is whether this is normal battery self-discharge (which shouldn't be more than 1-2% monthly for decent LiFePO₄) or something systemic. I'm currently trying a Victron SmartShunt to get granular data on what's happening between dusk and dawn.

Worth knowing: Are you running 12V or 24V? What battery manufacturer? And crucially—are you actually measuring voltage drop or estimated capacity from the BMS display? The latter can be quite inaccurate.

Would be useful if others could share their actual overnight drain figures with comparable setups. Might help establish what's normal versus what needs investigating.

That overnight drain is likely your BMS itself—LiFePO₄ packs draw 0.5-2% capacity per 24hrs in standby depending on the quality of the management board. Combined with any parasitic loads (inverter standby, voltage monitors, etc.), you're easily hitting that 10-15% figure.

Worth checking:

• BMS quiescent current: Victron Smart BMS units are transparent about this; cheaper Chinese boards are black boxes
• Inverter mode: Leave it in eco/search mode rather than always-on
• Voltage monitor drain: Some budget units pull 20-50mA permanently

On 200W generating capacity, you're fighting an uphill battle through winter months anyway. If you're static long-term, bumping to 400W is more realistic for reliable van living, especially if you're running heating or serious water pumps.

What's your actual load profile when parked up? That'll determine whether the overnight loss is purely the battery's internal consumption or something else entirely.

Mate, 10-15% overnight is criminal—that's either your BMS being chatty or you've got a phantom load sneaking about. Check your Victron's night consumption on the app (if you've got one) and see what's actually pulling. Also, what's your cutoff voltage set to? If you're not letting the battery sleep properly, it'll bleed like a stuck pig. On my shepherds hut I had similar grief until I realised the inverter was drawing 40W just existing. Throw a clamp meter at everything before assuming the battery's dodgy.

Right, couple of things to check before you assume the worst:

First, what's your actual load profile? Fridge running? Phone charger left plugged in? Inverter in standby? Those sneaky buggers add up quick.

Second—and @ThistleTel's spot on here—measure the pack voltage at night. If it's dropping steadily but the BMS isn't cutting off, you've got a phantom load. If it's holding steady then dropping suddenly at dawn, that's just the BMS being pedantic about balancing.

I run a similar 100Ah LiFePO₄ in my cabin setup. With everything genuinely off, I lose maybe 2-3% overnight. 10-15% suggests something's drawing current you're not accounting for.

Get a multimeter on the main positive line with everything "off"—if you're seeing more than 50mA, you've found your culprit.

Hi @FormerMariner1, that does sound frustrating. Before you panic though, have you actually measured what's happening with a meter?

10-15% seems quite high even accounting for BMS standby, so I'd be looking at:

1. Phantom loads - check if your leisure battery isolator is properly disconnecting, or if there's a charger/converter still drawing power when parked up
2. Temperature - LiFePO₄ capacity readings get dodgy in cold weather; you might be losing less than it appears
3. BMS settings - some aftermarket packs have overly aggressive balancing that runs overnight

Worth also checking what your actual voltage drop is over 8 hours rather than just relying on the battery's percentage display. Gives you a clearer picture.

What's your setup—integrated BMS or external? And are you seeing consistent drain every night?

Linda

200W into 100Ah is a bit like bringing a teaspoon to a knife fight—your array barely keeps pace with daytime consumption, let alone charging. Overnight drain sounds like you're either running essentials (fridge, habitation stuff) or your Victron kit is doing the vampire routine with comms/monitoring.

Quick thought: what's your BMS reporting versus what an external shunt meter says? They can drift spectacularly. Also, 10-15% overnight on LiFePO₄ isn't catastrophic if you're genuinely idle, but it's worth measuring actual load with a clamp meter when everything's supposedly off.

Honestly though, 200W for a van is undersized if you're running anything with a pulse. Seen too many people discover their "minimal loads" are actually quite chatty.

@FormerMariner1 worth noting that "minimal loads" is doing a lot of work in that sentence. A basic 12V compressor fridge alone pulls 3-5A average — that's 30-60Ah overnight easily. Add any inverter standby draw, a Victron MPPT or BMV with Bluetooth active, even a phone charging, and your 10-15% loss starts looking optimistic rather than suspicious.

Also, what BMS are you running? Some cheaper LiFePO₄ cells (especially the grey-market 100Ah packs flooding eBay) have parasitic drain issues that only show up when you actually measure at the terminals with a clamp meter.

@LazyRanger makes a fair point about array sizing, but I'd sort out where the drain is actually coming from before throwing more panels at it — you might just be masking the real problem.