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

Short drives in winter are genuinely brutal for keeping anything topped up. The alternator barely gets a chance to do meaningful work before you're parked up again, and with solar production in the UK being essentially a joke from November through February, it's a real squeeze.

I'm not in a motorhome myself — tiny cabin setup — but I helped a mate sort his van last winter and we ended up fitting a Victron Orion-Tr Smart DC-DC charger rather than relying on a basic split-charge relay. The difference was noticeable almost immediately. The Orion actually charges the leisure battery properly rather than just trickling whatever the alternator happens to throw at it. If you're still running an old VSR setup, that's probably your first problem.

A few things worth considering:

• Battery chemistry matters — AGM and lithium respond very differently to short charge cycles. Lithium in particular doesn't really suffer the same way.
• Parasitic loads — what's drawing from the battery when you're not driving? Even small drains add up over weeks of short trips.
• Shore power — even a basic hook-up once a week can save you if you have access to one.

Has anyone tried pairing a small roof panel with a decent MPPT (even something modest like a Renogy 100W kit) just to offset the winter deficit? Curious whether that's made a practical difference for people actually living in their vans rather than just weekend use.

What alternator output are you working with? Some of the older motorhome engines are surprisingly stingy and that makes the whole situation worse before you've even factored in the weather.

@StormyMender this is exactly what pushed me down the lithium rabbit hole two winters ago. Had a 100Ah AGM that would just laugh at a 20-minute motorway hop — acceptance rate so poor it barely registered.

Switched to a Fogstar Drift 100Ah LiFePO4 and the difference was remarkable. Lithium will genuinely gulp down whatever the alternator throws at it during those short runs, whereas AGM chemistry physically can't absorb charge fast enough.

Worth checking whether you've got a basic split-charge relay or a proper DC-DC charger (B2B) in the mix too. A relay on a modern smart alternator is practically useless — the Victron Orion-Tr Smart changed everything for me. Even a 15-minute drive puts a meaningful dent in the deficit now.

Winter solar in Scotland is basically decorative, so every amp from the engine counts.

Worth flagging that the alternator issue isn't just about drive duration — most vehicle alternators see the battery as "full" far too early with AGM, and especially with lithium, so you're not actually getting the amps you think you are.

A DC-DC charger (B2B) is the proper fix here. Victron Orion-Tr Smart is the obvious choice, isolates the starter battery properly and you can programme charge profiles. Even a 30A unit will do meaningful work on a 20-minute school run.

I fitted one to a static setup as emergency backup and the difference in winter charging efficiency was immediately obvious compared to relying on a direct split-charge relay.

Split-charge relays are essentially useless for lithium anyway — the voltage differential never triggers them correctly in cold weather. If you're still running one, that's likely your real problem regardless of battery chemistry.

Not a motorhome setup myself — static caravan and cabin — but the underlying problem is identical when I'm running a generator for short bursts rather than driving.

What nobody's mentioned yet: voltage drop across the B2B charger wiring is absolutely killing efficiency on short runs. If your cable run is undersized, you're losing meaningful amps before they even reach the battery. I ran 16mm² the full length on my cabin feed and the difference was measurable.

Also worth considering a Victron Orion-Tr Smart in non-isolated mode if your vehicle chassis is shared earth — the isolated version is often overkill and introduces slightly higher losses. The Orion's adaptive algorithm at least prioritises bulk charge aggressively during those brief windows you do get.

@RetiredPlumber makes a fair point about alternator perception of charge state — that's exactly why a proper DC-DC unit matters over a simple relay split-charge.

@RetiredPlumber makes a solid point about alternator sensing, and it's worth adding the practical fix: a DC-DC charger (B2B) completely sidesteps that problem. Units like the Victron Orion-Tr Smart isolated 30A will actively draw from the alternator at a controlled rate regardless of what the vehicle's smart charging system thinks it's doing.

Running one of these into a Fogstar Drift 100Ah LiFePO4 here, and even a 20-minute motorway stint in December is delivering 8-10Ah reliably. The key difference versus a split-charge relay is that the B2B maintains a proper charge profile — your lithium (or AGM) actually gets charged, not just connected to whatever voltage the alternator decides to present that day.

Budget around £150-200 for a decent isolated unit. Non-isolated versions exist cheaper but I wouldn't bother with anything other than isolated in a vehicle install.