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

Winter driving is a proper pain for keeping charge up — I spent last January scratching my head wondering why my 200Ah Fogstar lithium was barely hitting 70% despite doing a decent run each day.

Turned out my alternator-to-battery setup wasn't the issue so much as short stop-start driving. The B2B charger (running a Victron Orion-Tr Smart) needs time to actually do its thing, and if you're doing 20-minute hops between villages it barely gets going before you've killed the engine.

A few things that helped me:

• Upped my solar — added a 200W flexible panel to the roof last autumn. Even on grey Northumberland days it chips in something
• Pre-conditioning — if I know I've got a cold static night ahead, I'll run the engine for 20-30 minutes on arrival rather than just parking up
• Checking the alternator output temperature — cold alternators throttle back more than people realise

The honest truth though is that short winter trips and lithium don't play brilliantly together. The B2B chargers help enormously compared to a direct split-charge relay, but they're not magic.

Anyone running a DC-DC charger set to a higher absorption voltage to compensate? I've been tempted to nudge mine up slightly but haven't pulled the trigger yet — nervous about doing anything daft.

What's everyone else's experience — are those of you with AGM finding it worse, or is lithium actually the bigger headache here?

@Geordie split charging via alternator is notoriously poor for lithium in winter — your alternator's outputting less anyway due to cold, and without a proper DC-DC charger (B2B), the BMS likely keeps throttling it back.

I run a Victron Orion-Tr Smart 30A on my boat and it transformed winter charging completely. It conditions the charge properly rather than just dumping raw alternator voltage at the battery.

Worth checking:

• Is your B2B sized correctly for your 200Ah bank?
• Are you running any parasitic loads while driving?

A 30-minute winter drive genuinely won't cut it regardless — lithium wants consistent current over time. I'd also look at whether your alternator has a smart alternator (common on newer vehicles), which complicates things further and makes a B2B essentially non-negotiable rather than just recommended.

@Geordie @SimonThompson is right about the alternator limitations, but worth drilling into why it's worse in winter specifically — cold lithium cells have significantly elevated internal resistance, so even if your B2B charger (assuming you're running one) is pushing full current, the battery's acceptance rate drops sharply below around 5°C. Your Fogstar cells are probably throttling charge acceptance automatically as a protective measure.

The real fix I found was fitting a Victron Orion-Tr Smart 30A DC-DC charger — it handles the voltage curves properly and you can monitor what's actually being accepted via the VictronConnect app. Watching real-time charge current showed me the battery was refusing anything above 8A when cold.

Pre-warming the battery compartment slightly before driving makes a measurable difference too — even insulating the battery box properly recovered a noticeable chunk of acceptance rate for me.

@Geordie had almost identical issue with my setup last winter — what actually sorted it for me was fitting a DC-DC charger (went with a Victron Orion-Tr Smart 30A). The difference was night and day compared to relying on a split charge relay.

The relay was essentially just passing through whatever the alternator managed, but the DC-DC properly regulates the charge profile for lithium chemistry regardless of what the alternator's doing.

Worth checking what @SimonThompson and @CrafterConvert are hinting at too — are you running a B2B charger or just a VSR/relay? That's often where people go wrong. A relay made sense for lead-acid but it's genuinely not fit for purpose with lithium.

What's your current charging setup between the starter and leisure battery?

Really good thread this. @NotAnElectrician is spot on about the DC-DC charger — made a massive difference to my setup too. One thing worth adding that nobody's mentioned yet: check your alternator isn't going into thermal protection mode on short runs. In winter, the alternator takes ages to reach proper operating temperature, so you're often only getting a fraction of its rated output during the window you actually need it. Also worth looking at your cable runs — voltage drop becomes more significant when you're already fighting reduced alternator output. I swapped to a slightly heavier gauge on my B2B charger feed last winter and picked up a noticeable improvement. With lithium especially, you want every volt you can get reaching the charger efficiently rather than disappearing as heat in undersized wiring.

@Geordie don't forget lithium needs a solid absorption stage to push past 80% — your alternator's basically given up and gone home for a brew before it even gets there on a short run. 🔋

Worth checking if your van has smart alternator (variable voltage) tech too — mine was throttling output so aggressively the Victron Orion-Tr Smart I eventually fitted felt like a revelation. Goes from "barely charging" to "actually doing the job" remarkably fast.

Cold batteries also want higher voltage to accept charge properly, so winter stacks the odds against you doubly. The Orion handles that negotiation so you don't have to.