Anyone else struggling to keep leisure batteries topped up on short winter drives?

Been battling this exact problem since October. My van conversion runs a 200Ah Fogstar lithium bank and even with a B2B charger inline, the short commute-style drives I'm doing just aren't cutting it. Engine barely gets warm before I'm parked up again, and the alternator's hardly breaking a sweat.

The real kicker is that winter sun is so pathetic here in the north that the 400W roof array is producing maybe 15-20% of its rated output on a good day. So I've got two charging sources both essentially limping along simultaneously.

What's changed my situation somewhat is setting the B2B charge current higher during that brief window when the engine's running — I've got a Victron Orion-Tr Smart and tweaking the absorption settings made a noticeable difference. Still not perfect, but it claws back a bit more per journey.

I've also started plugging into hook-up at home once a week using a basic mains charger, which feels like admitting defeat but genuinely keeps things stable through the darker months.

Curious whether anyone's gone down the DC-DC charger upgrade route — moving from a 20A unit to something beefier — and whether it actually shifts the needle in real-world short journeys. Also wondering if anyone's added a second alternator or done a split-charge relay setup alongside a B2B, because that sounds like overengineering but maybe I'm wrong.

What are others doing to survive January and February without constantly nursing a half-flat bank?

@Gazza this is a well-documented limitation of B2B chargers that doesn't get discussed honestly enough. The issue isn't your charger's efficiency — it's the ramp-up time. Most B2B units (Victron Orion-Tr Smart included) spend the first few minutes negotiating with the alternator before delivering meaningful current. On a 15-minute run you might only get 8-10 minutes of actual bulk charging.

On my narrowboat I face the same problem with engine-charging sessions. What transformed things was setting a higher absorption target and accepting the B2B will never fully top lithium in short bursts.

Practical suggestions:

• Shore power whenever moored/parked, even briefly
• Check your B2B's engine-detection threshold — sometimes raising it reduces ramp delay
• Consider a small mains inverter-charger as primary, treating the alternator as supplementary

What's your B2B rated at versus your alternator output?

@Gazza welcome to the forum — glad you found us, this is exactly the kind of real-world problem worth digging into.

Something that genuinely transformed my winter situation was adding even a modest rooftop solar panel to sit alongside the B2B. My van runs a 175W Renogy panel and on a clear December day it'll contribute meaningfully even when parked up — which is often when I'm not driving anyway.

The two sources together tell a much better story than either alone. Short drives top up something, solar covers the static hours.

Worth also checking your B2B's bulk charge settings — my Victron Orion had a few tweaks available that made short-run charging noticeably more aggressive before dropping to absorption. Small gains, but they stack up across a British winter.

@Gazza mate, your B2B charger is basically doing the automotive equivalent of someone jogging to the fridge and back and calling it cardio 😂

Seriously though — short runs in winter are brutal. Your alternator's barely warmed up before you're parked again, and lithium doesn't care how hard you tried.

Few options worth considering:

@Gazza same boat here — literally. Running a 200Ah bank in my motorhome and short winter hops are basically useless for charging.

Have you looked at what input threshold your B2B actually needs before it kicks in? Mine was sat dormant for the first 10 minutes of every journey because the alternator voltage hadn't stabilised. Complete waste.

Two questions worth asking yourself:

• What's your B2B rated at in amps?
• Are you running any solar as a backup top-up between drives?

Even a small 100W panel does surprisingly well on bright winter days when the van is parked up. Not a solution on its own obviously, but it takes the pressure off those short runs.

Also curious whether your Fogstar cells are genuinely low or if it's a BMS reporting issue — worth checking with a proper voltage reading rather than relying on the charger's display.