Anyone else finding 200Ah lithium isn't enough for winter van life?

Picked up a narrowboat recently so been lurking the motorhome threads seeing how you lot handle power — curious if the challenges are similar.

Mate of mine is doing full-time van life in a Transit Custom, running 200Ah Fogstar Drift lithium with 400W of solar on the roof. Summer was fine, but now we're into November he's regularly hitting low-state-of-charge warnings by morning. Draws roughly 30-40Ah overnight just on heating (diesel heater fan + phone charging + a bit of LED), but the panels are barely pulling 20-30Ah on a dull day.

He's not got room for more panels and doesn't want to run the engine just to charge. Is a DC-DC charger from the alternator his best shout for topping up on driving days? Or would bumping to 300Ah be the smarter long-term fix — he does maybe 40-50 miles a day so alternator time is reasonable. Using a Victron SmartSolar already so the monitoring side is sorted.

BrambleHermit | 847 posts | ⚡ Solar Enthusiast

@LochDweller Welcome from a fellow boat-curious member! Your narrowboat experience might actually be really valuable here — the principles are pretty much identical, just the form factor differs.

For your mate in the Transit, 200Ah sounds generous until you factor in that lithium's usable capacity drops noticeably below about 5°C. In a cold British winter he's potentially losing 15-20% right there before he's even switched the kettle on.

The bigger question is what's charging those 200Ah. A single alternator with no DC-DC charger won't keep up if he's stationary for days. Winter van life in the UK often means grey skies killing solar output AND short driving days.

Has he looked at his actual consumption figures, or is he just noticing the bank depleting faster than expected?

BoxerAdventure | 134 posts | 🔋 Off-Grid Learner

Not van life myself — I've got a static caravan setup and mostly think about emergency backup — but 200Ah does seem tight for full-time winter use from what I've read here.

Quick question for the thread though: does your mate have any solar on the roof, or is he relying purely on B2B charging from the alternator? I'm trying to understand whether the bottleneck is storage capacity or charging opportunity in winter months, because those seem like quite different problems to solve?

Also wondering whether a second 100Ah battery would actually help if the charging can't keep pace anyway. Has anyone here found that adding panels made more difference than adding capacity for winter specifically?

OffGridKing | 2,341 posts | ☀️ Off-Grid Veteran

@LochDweller Boats and vans actually share more challenges than you'd think, particularly around limited solar harvest in winter and high heating loads. 200Ah is genuinely tight for full-time living once you factor in a diesel heater running overnight — that alone can chew through 20-30Ah depending on the controller.

Your mate's best bet short-term is aggressive load management and understanding exactly where the power's going. A decent battery monitor (Victron BMV is the go-to) will reveal surprises pretty quickly.

Longer term, adding a second 100Ah battery is often cheaper than people expect, especially buying used cells from reputable suppliers. What's his alternator charging situation like? A properly sized DC-DC charger whilst driving can make a massive difference through the darker months when solar's barely contributing.

NorfolkSolar | 512 posts | ⚡ Solar Enthusiast

@LochDweller Great crossover question! One thing nobody's mentioned yet — winter van life really exposes how little usable solar you're actually getting. Your mate might have 200Ah nominal, but if he's only seeing 2-3 hours of decent generation on grey December days, he's fighting a losing battle regardless of battery capacity.

The honest answer is often not simply "get more batteries" — it's about auditing actual consumption first. Heating is usually the silent killer. If he's running a diesel heater, that's relatively efficient, but any electric heating will absolutely devour a 200Ah bank overnight.

Worth asking: what's his alternator charging situation? A decent DC-DC charger and regular driving can genuinely transform winter sustainability more than doubling battery capacity would.

Chopper62 | 847 posts | 🔋 Off-Grid Enthusiast

Your mate's probably running into the classic winter trap — 200Ah sounds plenty on paper but usable capacity drops noticeably in cold temps, and that's before accounting for shorter solar days. On my van setup I found the real game-changer wasn't adding more battery capacity, it was auditing what's actually drawing power. Diesel heater on low overnight was my biggest surprise culprit when I finally stuck a proper monitor on it.

@LochDweller interesting you mention the narrowboat — I'd imagine your charging options are actually better than a static van since you can run the engine more naturally as part of daily life rather than feeling like you're specifically "running it to charge." Does your mate have shore power access at all during winter, even occasionally?

ExChippie94 | 287 posts | 🔧 Tinkerer

Been on a narrowboat for two years now and yeah, 200Ah lithium was my starting point too — upgraded to 400Ah pretty quickly once winter hit. The dark months absolutely batter you.

Big thing nobody's said yet: inverter loads are the silent killer. Kettle, microwave, induction hob — even brief spikes hammer your usable capacity faster than you'd think. I run a Victron Multiplus and it showed me exactly how bad my habits were once I actually logged it.

@LochDweller your mate in the van probably needs to audit what he's actually drawing before just throwing more Ah at the problem. Fogstar cells are decent value if he does end up upsizing though, done well by me on the boat.

BurnKen | 134 posts | 🔋 Off-Grid Enthusiast

@LochDweller the van/narrowboat comparison is more relevant than people think — both suffer the same fundamental winter problem of short days killing your solar input right when you're using the most power. One thing worth flagging to your mate that hasn't come up yet: parking/mooring orientation matters enormously in December. A Transit facing the wrong direction on a cloudy site might as well have no panels at all. Sometimes a simple repositioning habit gains you more than upgrading batteries. What's his typical overnight location situation — urban streets or more rural?

HighlandOffGrid | 634 posts | 🏔️ Off-Grid Veteran

@LochDweller Interesting crossover indeed! One thing worth considering for your mate specifically — Transit vans lose heat so rapidly compared to narrowboats that the heating system ends up cycling far more frequently, which absolutely hammers the battery. On the boat you've got much better thermal mass working in your favour.

For van life specifically, a decent quality diesel heater with a timer pre-warming the van before bed makes a surprising difference to overnight consumption. Reduces how hard the heating works when you're actually sleeping.

Also worth asking your mate what his actual resting voltage looks like at dawn — that'll tell you whether it's genuinely a capacity problem or a charging problem.

WattLiz | 134 posts | ☀️ Solar & Motorhome

Really relevant thread for me — running 200Ah Fogstar Drift in my motorhome and winter does expose the gaps. One thing worth flagging to your mate: what's his charge sources split looking like? Solar obviously suffers badly December/January, but if he's not maximising alternator charging with a proper DC-DC (B2B) charger, he's leaving easy amps on the table during driving hours.

Is he stationary for long periods or moving regularly? That changes the whole strategy. Also curious — @ExChippie94 what did you upsize to on the narrowboat? Wondering if the consumption patterns are actually that different.

TIW_Power | Array | ☀️ Solar Enthusiast

200Ah is genuinely marginal for full-time winter use — the solar input side is what kills you more than the battery capacity itself. Your mate's Transit will be lucky to get 1-2 usable hours of decent generation some December days in the UK, so even a perfectly sized bank just isn't getting topped up.

@LochDweller the narrowboat angle is interesting — at least you've got the option of shore power at most marinas, which takes the pressure off entirely. Van dwellers don't always have that fallback.

Personally I'd be looking at whether the alternator charging setup is optimised before throwing more battery at the problem.

NickThompson65 | 287 posts | 🔋 DIY Enthusiast

@LochDweller the narrowboat comparison is actually quite apt — a mate runs a 60ft widebeam and faces identical headaches come November. One thing nobody's mentioned yet: thermal management of the batteries themselves matters more than raw capacity in winter. A 200Ah bank that's sitting at 5°C is effectively a smaller bank — lithium BMS protection cuts charge acceptance right down in the cold. Worth checking whether your mate's Transit has any insulation around the battery compartment. Sometimes that's a cheaper fix than jumping straight to a bigger bank.

OakSpirit | Array | 🚐 Van & Narrowboat

@LochDweller narrowboat is actually harder in some ways — you can't just drive somewhere sunny to top up, and shore power isn't always available on moorings.

200Ah lithium on my boat was marginal until I sorted the charging sources properly. The issue usually isn't capacity, it's charge rate — a single 40A DC-DC charger from the engine alternator means you're only putting in ~200W whilst cruising. Add a Victron MPPT and prioritise reducing loads before adding more cells.

What's the inverter situation on the Transit? That's often where the power disappears.

PanelChris | 412 posts | ☀️ Solar & Motorhome

The bit people consistently underestimate is usable capacity in cold weather — lithium BMS protection means you're often working with less than you think when temps drop properly. Your mate might find he's only pulling 160-ish Ah realistically on a bitter January night.

@NickThompson65 makes a fair point about the narrowboat parallel — both situations reward having a secondary charging source sorted. For the van context, a decent B2B charger fed from the alternator whilst driving makes a surprising difference to winter sustainability. Even short runs add up across a week.

RockyCaptain | 156 posts | ⚡ Off-Grid Builds

@LochDweller your mate's Transit issue is almost certainly not the 200Ah itself but what's charging it in winter. Short grey days mean solar barely touches the surface, and if he's relying on that alone he'll be perpetually half-empty. A DC-DC charger properly wired to the alternator changes everything for van life — even a 30-minute drive makes a meaningful dent. 200Ah is workable for one person if the charging side is sorted. What's his current setup for replenishment? That'd help diagnose whether it's a capacity problem or a charging problem.