Anyone else struggled to keep a 100Ah lithium topped up on a cloudy week in Scotland?

Lived this exact nightmare last October up near Loch Lomond. Three days of proper grey soup overhead and my 100Ah Fogstar Drift just sat there at 62% laughing at me.

The problem I found wasn't really the battery — it was my single 175W panel doing absolutely nothing useful between 9am and 3pm because the angle was wrong and the cloud was relentless. I'd convinced myself that diffuse light would be enough to keep on top of things. It is not. Scotland does not do diffuse light. Scotland does dark.

What saved me was eventually caving and running the engine for 40 minutes each morning through a DC-DC charger (Victron Orion-Tr Smart — genuinely brilliant bit of kit). Not ideal, not what I planned, but it kept the fridge ticking over and the lights on.

Since that trip I've added a second panel and tilted both properly. Makes a surprising difference even in miserable conditions.

A few things worth considering if you're heading north:

• Tilt your panels — flat-mounted on a motorhome roof in Scotland is basically decorative
• Oversizing your solar matters far more in the UK than the calculator spreadsheets suggest
• A small DC-DC charger as backup is genuinely worth the install cost

Curious what others are running up there. Are people going bigger on battery capacity instead, or tackling the solar side? I sometimes wonder if a 200Ah bank would've just delayed the problem rather than solved it.

@Nessa68 — Scotland in October is basically a solar panel's worst nightmare, and 62% on a Fogstar Drift is actually not terrible considering!

The issue most people don't realise is that usable capacity drops dramatically once you factor in voltage sag under load. At 62% SoC you're already losing efficiency on anything drawing serious current.

What sorted my Scottish trips was adding a DC-DC charger (I use a Victron Orion-Tr Smart 30A) wired to the alternator. Even a 90-minute drive to a village shop puts back 8-10Ah reliably — grey skies irrelevant.

Also worth checking your panel's actual output with a Victron SmartSolar MPPT rather than guessing. Mine was producing 11W on a genuinely overcast day with a 200W panel — sobering numbers that change your consumption habits fast.

@Nessa68 I know that Loch Lomond grey intimately. Did the same trip, different year, same miserable outcome.

What saved me eventually wasn't more panels — it was accepting that Scotland in autumn means solar is basically decorative. I run a small Honda EU22i as genuine backup now, not a last resort. Two hours of quiet running topped my 100Ah Fogstar right back up whilst I cooked dinner.

The mindset shift mattered more than the kit. Once I stopped treating the generator as admitting defeat and started treating it as part of the system, the whole trip changed.

Also worth checking your panel tilt. Flat-mounted on a van roof in October at Scottish latitudes you're losing a brutal amount of what little light exists. Even propping the front up 20° makes a measurable difference on the MPPT readout.

@Nessa68 genuinely painful reading this because I've had almost identical grief — not in a van but keeping my garden office battery topped up through a horrific grey February fortnight.

My question is: what's your panel wattage vs the 100Ah? Because I suspect that's where people go wrong — they size the battery first and bolt on whatever panels fit the roof afterwards.

Did you have any wind or shore power backup option at all? I keep wondering whether a small wind turbine makes any sense for Scottish trips specifically, given the... generous breeze situation up there.

Also curious whether the Fogstar BMS was cutting anything out or whether that 62% was just genuinely where generation matched consumption. Because those are two very different problems with very different fixes, aren't they.

@Nessa68 Scotland in October is basically the solar stress test nobody asked for. I run a modest 200W panel setup on my cabin and even down south a cloudy week will have me nursing the battery carefully.

The thing that genuinely saved me was adding a small DC-DC charger so I can top up from the alternator on driving days — even a 30-40 mile run puts a decent chunk back in. Victron's Orion-Tr Smart is brilliant for this and plays nicely with lithium profiles.

Also worth checking your Fogstar's actual resting voltage after those grey days — 62% displayed can sometimes be pessimistic if the BMS hasn't had a proper rest period to recalibrate. Might not be as dire as it looked on screen.

@Nessa68 The real culprit with that scenario is usually panel sizing relative to typical daily consumption — most van builds assume average UK irradiance figures that Scotland in autumn simply doesn't deliver.

What actually saved my setup was adding a DC-DC charger (I run a Victron Orion-Tr Smart) fed from the alternator. Even a 90-minute drive between spots can push 20-30Ah back into a Fogstar Drift. Combines nicely with whatever solar manages to scrape through the cloud cover.

Worth also checking your MPPT controller's absorption settings — in low-irradiance conditions some units will abandon the charge cycle prematurely, convinced the battery's full when it genuinely isn't. A Victron SmartSolar lets you adjust those thresholds via Bluetooth, which made a noticeable difference to my recovery times during a similarly grim week near Dumfries.