Swapped out the old split charge relay on my narrowboat – worth it?

Finally got round to upgrading the charging setup on our 35ft narrowboat after years of the engine alternator doing all the heavy lifting via a basic split charge relay. Replaced it with a Victron Orion-Tr Smart 12/12-30A DC-DC charger and honestly the difference is noticeable. Batteries are actually reaching a proper absorption stage now rather than just topping off at whatever voltage the alternator happened to be sitting at.

Running a 200Ah AGM bank at the moment (looking at lithium next season). Before the swap, the relay was just dumping raw alternator voltage – around 13.8–14.0V – straight into the bank whenever the engine was running. The Orion is now pushing a genuine 3-stage charge profile and I'm seeing it hit 14.4V absorption consistently on a 2–3 hour cruise.

Has anyone else made this switch on a boat, narrowboat specifically? Curious whether the improvement I'm seeing is mainly down to the DC-DC charger itself or partly because my old relay was just knackered. Also wondering whether it's worth adding a BMV-712 battery monitor alongside it, or whether the Victron app gives you enough info on its own through the Orion's Bluetooth.

Nessa61 | 847 posts

@NeilAllen great timing on this post! We made exactly the same switch on our 58ft last spring and the difference was night and day. The Orion's ability to properly bulk/absorb/float your leisure bank rather than just chucking alternator voltage at it blindly is worth the price alone in battery longevity.

One thing worth mentioning that caught us out initially – if you're running a smart alternator (quite common on newer Beta and Nanni engines), make sure you've got the non-isolated version wired correctly or you'll get some odd behaviour with the alternator sensing. Took us a frustrating afternoon to sort that one!

How are your leisure batteries looking health-wise? If they've been undercharged for years via the old relay setup they might not be holding a full charge anymore regardless. 🚢

@NeilAllen ooh this is timely, I've been mulling something similar but for a static setup rather than a boat. Does the Orion actually make a meaningful difference to charge acceptance on your leisure bank compared to the old relay? I always assumed the relay was "good enough" but I've read the voltage drop argument a hundred times and still can't decide if it's marketing fluff or genuine gains.

Also — what battery chemistry are you running? I've got Fogstar lithium in my garden office setup and I know the charging profile matters enormously compared to bog-standard AGM. Wondering if the Orion's programmable output is half the point of it really.

What alternator size are you working with? Some of the older narrowboat engines have quite modest alternators and I'd hate to see someone cook one chasing faster charging.

SarahFrost | 312 posts

@NeilAllen great upgrade choice! One thing worth mentioning that catches people out – make sure you've got the correct fusing right at the battery terminals on both banks. The Orion's input protection is decent but I've seen a few installs where folk skimped on this and regretted it. Also worth checking your alternator output – older narrowboat alternators can sometimes struggle with the Orion's demands if they're already a bit tired. Might be worth grabbing a clamp meter and monitoring charging current during your first few cruises.

@AnneOliver the Orion works brilliantly in static setups too, though for a non-mobile installation you'd possibly be better served looking at a dedicated mains charger or solar MPPT depending on your power sources – happy to chat through your specific situation if you want to start a separate thread!

ExpertBuild | 1,204 posts

@NeilAllen solid upgrade – the Orion-Tr Smart is a proper bit of kit. One thing I'd add that nobody's touched on yet: if you're running the engine at low revs while manoeuvring (which on a narrowboat is basically constant), your alternator voltage can drop enough that a standard relay simply disconnects. The Orion sidesteps this entirely because it's regulating the output voltage independently rather than just passing through whatever the alternator produces. Means your leisure bank gets a decent charge even during slow lock work.

@AnneOliver for a static setup the DC-DC converter approach is less relevant unless you're bridging two separate battery banks – worth clarifying your setup before going down this route, as there may be simpler options.

What leisure bank capacity are you running @NeilAllen, and are you pairing it with any solar?

Gazza81 | 847 posts

@NeilAllen nice one! Done exactly this on my 40ft widebeam about 18 months ago and haven't looked back. The big thing nobody mentioned yet – have a play with the adaptive charging algorithm settings in the Victron Connect app once you've got a few charge cycles under your belt. Out of the box it's fairly conservative, and depending on your battery bank type you might find tweaking the absorption voltage and tail current settings gets you noticeably better state of charge. Made a real difference for me once I dialled it in properly. Also worth checking your cable run lengths and sizing if you haven't already – the Orion is only as good as the installation around it. What battery chemistry are you running on the leisure bank?