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

Right, so I know this is the motorhome forum and I'm usually lurking from the static caravan corner, but hear me out — I spent three winters living mobile before I planted myself on a site, and the short-drive battery death spiral is exactly what drove me to rethink everything.

The problem is brutally simple. Your alternator barely gets the leisure battery above 50% on a 20-minute school run errand, then you're drawing from it all evening. Repeat for a week and you've quietly murdered a perfectly good battery through chronic undercharging.

What eventually sorted it for me (before I went static) was a Victron Orion-Tr Smart DC-DC charger rather than relying on a split charge relay. The relay is essentially useless in this scenario — by the time the voltage difference triggers it meaningfully, your drive's nearly done. The Orion actually charges the leisure battery properly from the alternator, even on shorter runs. Made a noticeable difference through a January in Northumberland.

Some people swear by adding a small solar panel on the roof to compensate — even a 100W Renogy panel will drip-feed enough to offset the losses if you're parked up during daylight. Not glamorous, but effective.

The other thing worth checking is your battery's actual state of health. If it's more than four or five years old and struggling in winter, it might just be on its way out regardless.

Anyone running lithium leisure batteries finding it's any better with the higher charge acceptance rates? Curious whether a Fogstar or equivalent actually holds up noticeably differently on the short-hop charging front.

@MoreTeaVicar the B2B (DC-DC) charger route is genuinely the answer here — a standard split-charge relay barely functions below about 13.7V alternator output which is exactly what you get on short cold runs when the engine ECU prioritises the starter battery.

Fitted a Victron Orion-Tr Smart 30A on the narrowboat and the difference was immediately obvious. It'll boost charge properly regardless of what the alternator's actually putting out.

Worth checking:

• Wire gauge from alternator to B2B — undersized cable kills efficiency fast
• Smart alternator? Needs isolation relay before the B2B input
• Battery chemistry — if you're running AGM or lithium the charge profiles differ massively

Fogstar do decent lithium options if you're considering upgrading the leisure bank whilst you're at it, which compounds the benefit of proper B2B charging significantly.

@PanelEwan I've been looking at the B2B route myself actually — currently running a 200Ah Fogstar lithium in the leisure bank and the alternator contribution on short runs is negligible.

Couple of questions before I commit to anything:

1. What amperage rating would you recommend for a typical 100A alternator setup? Is 30A sufficient or worth jumping to 40A?
2. Does the B2B cause any issues with modern smart alternators, or does it handle that automatically?
3. Any reason to prefer Victron Orion-Tr Smart over the Sterling alternatives?

My driving pattern in winter is mostly 20-30 minute hops between sites, so I genuinely can't rely on solar either at this time of year. Trying to work out whether the B2B pays for itself versus just plugging into EHU more frequently.

@BevJackson64 200Ah Fogstar sitting there like a disappointed toddler while you do a 20-minute school run — absolutely classic winter scenario 😄

Worth knowing the Victron Orion-Tr Smart (isolated version) will actually talk to the lithium's BMS rather than just lobbing electrons at it and hoping

@BoxerProject that "disappointed toddler" description is doing something to me 😂

Genuine question though — does the B2B charger size actually matter that much on short runs? I'm planning a garden office build rather than a van setup, but I've been eyeing a Victron Orion-Tr Smart for a potential mobile backup situation and wondering whether a 30A unit would recover meaningful charge in, say, 15–20 minutes of driving, or whether you're basically just offsetting the self-discharge and calling it a win?

Also does the alternator protection side of things concern anyone else? I've read conflicting stuff about newer Euro 6 engines with smart alternators not playing nicely with aggressive B2B draw — is the Victron handling that automatically or do you need to configure it carefully?