Anyone else struggling to keep a 100Ah lithium topped up just from driving in winter?

Short answer: yes, and it's not even close in December.

I'm running a 100Ah Fogstar Drift in the van and even with a decent B2B charger (Victron Orion-Tr Smart 30A), a 4-hour motorway run in November barely shifted the SOC from 40% to 75%. Engine alternator output drops, the B2B is fighting cold temperatures affecting charge acceptance, and you're simultaneously running the heater, fridge, and lighting anyway — so you're filling a leaking bucket.

The fundamental problem is that lithium needs proper bulk current to charge efficiently, and a typical alternator-fed B2B setup just doesn't deliver enough sustained current relative to battery capacity, especially on shorter trips or stop-start driving.

What's actually worked for me:

• Roof solar — even 200W of panels in winter gives you something, and on clear December days you'd be surprised
• EHU when available — obvious, but worth planning stops around hook-up sites more than in summer
• Lowering your consumption expectations — sounds defeatist but a diesel heater on eco mode vs full blast makes a massive difference overnight

Worth checking your B2B settings too. Some units default to conservative charge profiles. Also verify your alternator isn't being throttled by the van's smart charging system — VW and Ford Transit setups in particular can be awkward here.

Anyone running a larger B2B (40A+) or a second battery bank seeing better results? Curious whether it's worth upgrading the charger or just accepting solar is the only real winter fix.

Different beast but same battle — on the narrowboat I rely heavily on alternator charging via a B2B and winter is genuinely grim. Short cruising days, engine running cold, alternator not hitting full output until you've been moving a while.

Few things that helped me:

• Longer idle runs at the marina (engine on, boat going nowhere — controversial but effective)
• Dropping absorption voltage slightly so the B2B isn't fighting the BMS as hard
• Accepting the solar is basically decorative November–January 😅

@GoldenNomad a 30A Orion on a 4-hour run should be putting decent amps in though — worth checking your actual alternator output with a clamp meter. Some vans the alternator is just undersized from factory and throttles back hard when warm.

@GoldenNomad the Orion 30A is only pushing ~360Wh per hour at best, so your 4-hour run is delivering maybe 1.2–1.4kWh by the time you account for alternator warm-up, thermal derating, and the fact modern engines barely hold a decent charge voltage at idle or crawl speeds. On the narrowboat I've got the same battle — engine running for what feels like half the day just to recover what the fridge and heating controller ate overnight.

The maths simply doesn't work in winter without either a second charging source or dramatically cutting consumption.

Worth checking your Orion's Bluetooth logs — you'd be amazed how many people discover it's been sitting in bulk for 20 minutes then dropping to float because the BMS panicked. That alone explains a lot of "I drove for hours and got nothing" complaints.

@Boycie25 has done the maths well there. What nobody mentions is how much the alternator itself throttles back when the engine's cold — I noticed this up at the cabin last January, dead slow charging for the first 20–30 minutes while everything warmed up. Effectively losing half an hour of decent input on every run.

My workaround ended up being a small 100W panel on the roof running in parallel. Pathetic gain in December, yes, but even 20–30Ah across a grey day takes the pressure off the B2B having to do everything alone.

If your van's mostly stationary between drives, a solar top-up however modest genuinely changes the equation. The Orion alone was never designed to be the whole story.

@Boycie25 and @Slim3 have nailed the core issue, so I'll add what finally shifted things for me.

The game-changer wasn't a bigger B2B — it was accepting the van roof as the primary winter charger. I added a second 200W panel last January and now even on a gloomy English December day I'm pulling 20–30Ah by mid-afternoon. The Orion becomes top-up, not salvation.

Also worth checking: is your Orion set to lithium profile? Out of the box mine was defaulting to AGM. Was losing maybe 20% of available charge window before I spotted it.

The Fogstar Drift specifically will throttle incoming current if the BMS gets twitchy in the cold — seen mine drop to 10A acceptance on a bitter morning. Nothing's wrong, just physics.

Winter van life is a compromise. Anyone claiming otherwise is either lying or plugged into a hook-up. 😄

@LiFePO4Nerd go on then, don't leave us hanging like a dodgy shore power connection — what was the game-changer?

My narrowboat taught me the hard way that winter charging is basically a polite suggestion rather than a plan. Ended up slapping a 200W Renogy panel on the roof and suddenly the B2B isn't doing all the heavy lifting solo. Even weak December sun adds something while you're parked up at the services eating a disappointing pasty.

The real villain nobody mentions: if your 100Ah is already sitting low from the night before, that Orion's working against a deficit before you've even joined the motorway. Start fuller, finish fuller — revolutionary concept that took me an embarrassingly long time to grasp.

@EssexNomad seconding that — @LiFePO4Nerd has done the classic tease and vanished 😅

Anyway, my two penneth from the shepherd's hut world which isn't identical but the solar side translates — winter is genuinely brutal and I stopped pretending driving would save me.

What actually helped my van setup was adding even a modest 100W panel on the roof. Dead flat December days in the marshes here, you're scraping maybe 15-20Ah if you're lucky, but combined with whatever the B2B pulls on a run? You're at least competitive rather than just watching the Victron app make you sad.

The Fogstar Drift is solid but it can't magic electrons from nowhere. Sometimes the honest answer is the driving alone just won't cut it November–February and you need a second source in the mix.