Anyone else struggling to keep a 100Ah lithium topped up on short winter drives?

Been dealing with exactly this since October and it's properly doing my head in.

My setup is a 100Ah Fogstar Drift under the bed, fed by a 40A DC-DC charger from the alternator. On paper that should be fine, but my typical winter run is maybe 25-30 minutes to the shops and back — the charger barely gets through its bulk phase before I'm pulling up on the drive again.

A couple of things I've noticed that might be relevant:

• The DC-DC charger needs a good few minutes just to "wake up" and confirm the alternator is actually running before it starts pushing serious current
• Short stop-start routes (traffic lights, roundabouts) seem to confuse mine occasionally
• Heater, heated screen, lights — the van's own 12V loads are eating into what the alternator can spare

I've been compensating with a small 100W panel on the roof but obviously in December that's giving me next to nothing on most days. Honestly thinking about bumping up to a 200W panel just to have something coming in during daylight.

Has anyone found that a higher-rated DC-DC charger actually helps in this situation, or is the limiting factor really just time rather than current? I've seen some people running 60A units but I wonder if the van's wiring becomes the bottleneck before you even get there.

Also curious whether anyone has experimented with a mains hookup timer at home just to keep things topped off through winter — seems like the sensible backup option but feels like admitting defeat somehow.

What's everyone else doing to manage this?

@Clive1978 classic winter trap — the maths looks fine until you account for how little charge actually goes in on a 20-minute commute-length drive.

Your 40A DC-DC is the right tool but it needs time to work. First 5-10 minutes it's ramping up, then you've maybe got 15 minutes of actual bulk charge before you're parked again. You're probably getting 8-10Ah per short trip at best.

The real fix:

• Add solar if you haven't — even a 100W panel does meaningful work on a bright winter day
• Check your DC-DC is actually hitting 40A (Victron app or a clamp meter — don't assume)
• Reduce parasitic loads; fridges and inverters on standby are silent battery murderers

Also worth checking the Fogstar Drift's low-temp cutoff — below about 5°C some units throttle charging automatically. Could be masking the actual problem entirely.

@Clive1978 curious what your solar situation is like? Even a small panel — 100W or so — can make a surprising difference in winter if you're parked up for any length of time between drives. I've got a similar Fogstar setup on my shepherd's hut and found that combining even modest solar with the DC-DC meant the battery rarely dipped below 70% through December.

Also worth checking — is your DC-DC charger set to the correct lithium profile? Sounds obvious but I've seen a few people running theirs on a AGM setting and wondering why charge acceptance is poor. What does your state of charge look like when you actually set off in the morning?

@Clive1978 had almost identical frustration last winter with my setup. The thing that shifted things for me was checking what voltage my DC-DC was actually seeing from the alternator — mine was cutting out earlier than expected because the alternator voltage was drooping under load. Worth logging it properly if you can.

Also, have you checked your Fogstar's state of charge before you set off? If you're already drawing from it overnight for heating etc., you might be starting each drive from a lower baseline than you realise. A 40A charger sounds generous but if you're only getting 15-20 minutes of actual charge acceptance before you're parked up again, it adds up to very little over a week.

@Clive1978 the bit nobody mentions: a 40A DC-DC charger doesn't actually pull 40A unless the alternator and wiring can support it properly. Check your voltage at the charger input while driving — if it's sagging below 13.5V you're getting nowhere near rated output.

Also worth looking at your actual consumption overnight. Run a Victron BMV or similar for a week and you'll probably find you're drawing more than you think. Heating controllers are notorious for phantom loads.

Short winter drives are genuinely rubbish for keeping lithium topped up — there's no magic fix there. @CornishBoater is right that even 100W of solar takes the edge off, but only on decent days which, let's be honest, aren't exactly plentiful in winter.