Victron Orion-Tr Smart 30A vs 18A — worth the extra £60 for a narrowboat setup?

After a winter of running a 12v 200Ah Fogstar Drift LiFePO4 as my domestic bank from the engine alternator, I'm finally retiring the old split-charge relay and going proper isolated DC-DC. The relay was doing my battery no favours — big voltage dumps every time the engine fired up, and I suspect the BMS was tripping more than I realised.

I've been looking hard at the Victron Orion-Tr Smart isolated range. The 12/12–18A (220W) is around £130, the 12/12–30A (360W) is closer to £190. On paper the 30A sounds obvious, but my engine alternator is only a 65A unit and I've got a fairly modest 12v start battery with no smart alternator complications — so the 18A would cap me at roughly 216W input which isn't pushing it unreasonably.

The thing is, I'm planning to add a second 200Ah Fogstar cell later this year to bring the domestic bank to 400Ah. At that point, charge time off the engine becomes more relevant — canal running days are often only 2–3 hours. Would the 30A meaningfully shorten bulk charge time on 400Ah, or am I just throwing money at a marginal gain given I've also got a 400W solar array topping things up?

Has anyone actually run the 18A on a 400Ah+ bank and found it adequate, or did you regret not sizing up from the start?

@FenlandSolar on a nb the 30A is worth it imo. When you're cruising the cut you want to make the most of engine hours — especially winter when solar's useless. The 30A will push ~360W into your Fogstar vs ~216W with the 18A, so shorter runs to hit the same SoC.

I ran the 18A for about 8 months on my boat and swapped up. The difference on a 4hr cruise is noticeable, particularly if you're wild mooring away from shoreline.

One thing to check — what alternator are you running? Older BMC/Beta engines can have weedy 65A alternators and the 30A will be pulling nearly half that before hotel loads. Might want the Victron alternator protection feature enabled regardless.

The £60 over a few seasons is nothing really.

@BenJohnson95 has a point, but my static caravan "narrowboat experience" is just me pretending the Fogstar needs more charging while I watch Bargain Hunt — the 30A wins purely because regret is more expensive than £60.