Victron Orion-Tr Smart 30A vs 18A – worth the extra £60 for a shepherd's hut build?

Mid-way through wiring up my off-grid shepherd's hut and trying to nail down the DC-DC charger setup. Running a 200Ah Fogstar Drift LiFePO4 as the house bank, charged via a 200W Renogy panel on the roof and also wanting to top up from the Land Rover Defender's alternator when I tow it to site. The Victron Orion-Tr Smart isolated 12/12 18A sits around £120, the 30A version is pushing £180 – trying to work out if the extra grunt actually matters in real-world use.

The hut mostly lives on site so the solar handles the bulk of charging day-to-day. Alternator charging is really a "topped up before we arrive" scenario – probably 45–60 minutes of driving at most. At 18A that's roughly 16Ah pushed in, at 30A you're looking at 27Ah over the same run. With a 200Ah bank that difference feels marginal unless the battery is genuinely depleted.

One concern is the Defender's alternator – it's the older 90A unit and I've read that the Orion-Tr 30A can cause grief with smaller alternators if there's no proper ramp-up, even with the Orion's built-in current limiting. Anyone actually seen alternator stress with the 30A on a similar-sized alternator, or is that mostly scaremongering? The Victron BMS integration through VE.Direct is a big draw for me either way.

Has anyone gone back and wished they'd sized up (or down) after fitting one of these?

@Macca64 the 30A question always comes down to one thing for me — what's your alternator situation?

I spent weeks agonising over the same decision on my narrowboat build. Ended up going 30A and honestly, with LiFePO4 the charger works hard because the battery just hoovers up whatever you throw at it. An 18A unit on a Drift will throttle back before you've even made a brew.

The maths that swung it for me: 30A × 12V = 360W of charge capability. On a shepherd's hut where solar is your primary source, that alternator top-up when you're running a vehicle nearby could be the difference between a functional evening and a dim one.

£60 spread across the lifetime of the install? Genuinely nothing.

The caveat — if your leisure feed cable run is long, check your voltage drop first or the 30A rating becomes theoretical anyway.