Anyone else struggling to keep a 100Ah lithium topped up just from solar on a cloudy Scottish trip?

Just got back from two weeks in the Cairngorms and my Fogstar Drift 100Ah was basically living its worst life the entire time — four consecutive grey days had it sitting at 62% wondering what the sun even is.

Ended up leaning on the alternator more than I'd like to admit, which feels like defeat honestly. My Victron SmartSolar was logging some genuinely tragic numbers — we're talking 180Wh on a "good" day. Scotland in October is basically a solar panel's version of a bad dream.

Few things that saved me:

• Dropped my EV charger habit entirely (yeah, the van-to-car trickle setup had to take a holiday)
• Cut fridge to eco mode
• Started treating every sunny 20-minute window like it was a precious resource

Honestly makes me think 100Ah is just undersized for Scottish touring without at least 200W of panels minimum, ideally more. Anyone running a second battery up there? Curious whether folk are going 12V parallel or jumping to 24V for efficiency gains — I've been going back and forth on this for months and the Cairngorms trip finally broke my indecision.

Also — has anyone tried a Renogy DC-DC charger properly integrated so the alternator topping-up doesn't feel quite so shameful? 😅

What's everyone else's Scottish winter solar survival strategy?

@DaleLover mate Scotland doesn't so much have "weather" as a personal vendetta against solar panels 😂 — I'd throw a Victron SmartSolar on there so at least you can watch the misery in real-time via Bluetooth.

@DaleLover Did a similar run through Rannoch Moor last autumn in my Transit. Three days of that haar and my 100Ah Fogstar was in the same sorry state.

What sorted it for me wasn't more panels — it was finally wiring in a proper Victron Orion-Tr Smart DC-DC charger off the alternator. Even a two-hour drive to the next spot puts a meaningful chunk back in. Scotland practically forces you to drive somewhere eventually anyway, so you might as well harvest it.

Solar alone up there between October and March is basically decorative. Nice to have, occasionally useful, rarely reliable. Anyone who tells you otherwise hasn't actually been to Aviemore in November staring at 47% and rationing the kettle.

Plan for the alternator first, treat solar as the bonus it actually is.

@DaleLover had the same drama with my tiny house setup last winter — cloudy weeks are brutal on a single 100Ah. Honestly the fix that saved me was just accepting solar alone isn't enough as a sole source in Scotland and adding a small DC-DC charger from the vehicle alternator as backup. Even a 20A Victron Orion keeps things ticking when the panels are doing nothing useful.

Also worth checking your panel angle — steeper tilt helps massively with low winter sun, even on overcast days it catches more diffuse light than a flat mount will.

62% isn't disaster territory for a Fogstar Drift though, those cells are fine well below that. Just watch you're not pulling heavy loads when it dips under 20%.

@DaleLover the Cairngorms in shoulder season is genuinely a worst-case scenario for solar yield — I've got a static caravan setup near Aberystwyth and even Wales humbles me regularly, so Scotland must've been savage.

Worth actually logging your daily Wh intake rather than just watching SOC drift — a Victron SmartShunt paired with the app will show you exactly how bleak those harvest numbers are, which at least helps you plan. My caravan pulls maybe 180–220Wh on a proper grey day when I'm also trying to trickle-charge the EV overnight, which is... not ideal.

One thing that transformed my resilience was adding a second 100Ah rather than chasing bigger panels — you're essentially doubling your buffer for the same poor harvest. Storage capacity in overcast climates often matters more than peak generation.