Swapped out my old alternator for a DC-DC charger – worth it for leisure batteries?

Did exactly this on my narrowboat about eighteen months ago and honestly it transformed how my battery bank behaves.

Previously I had a standard 70A alternator dumping straight into my leisure bank — a mix of AGM batteries that never seemed to get properly topped up on the move. The alternator would throttle back once it sensed a surface charge, leaving the batteries sitting at maybe 80% for hours. Classic lazy charging.

Fitted a Victron Orion-Tr Smart 30A DC-DC between the engine battery and the leisure bank, and the difference was immediately obvious. The Orion doesn't care about surface charge — it runs a proper multi-stage profile all the way through absorption. After a decent cruise my Fogstar lithiums are sitting at 98-99% rather than that frustrating plateau.

A few things worth knowing before you jump in:

• 30A isn't massive — if you're running a big bank you might want to look at the 50A unit or run two in parallel
• You'll want to check your alternator isn't going to get hammered — DC-DC isolators it a bit, which actually protects older alternators from lithium's hungry bulk stage
• Wiring routing on a narrowboat can be fiddly depending on where your engine bay sits relative to your battery compartment

The Orion app via Bluetooth is genuinely useful for checking what's happening in real time, rather than guessing.

Would say it's absolutely worth it if you're doing multi-day cruising rather than just occasional weekend trips. Has anyone gone down the Sterling B2B route instead? Curious how those compare in practice.

@VanNicola curious what DC-DC charger you landed on? I've been eyeing up the Victron Orion-Tr Smart 30A for my static caravan's boat-adjacent setup (long story involving a marina berth and questionable life choices).

My main hesitation is whether 30A is actually enough to make a meaningful dent in a 200Ah LiFePO4 bank during a typical engine run. Do you find you need to run the engine specifically to charge, or does it tick things over passively while you're cruising anyway?

Also — does the Bluetooth monitoring via the Victron app actually work reliably on a metal-hulled boat, or does it turn into a game of "stand in exactly the right spot holding your phone like a divining rod"? 😄

@VoltPaddy the Orion-Tr Smart 30A is solid but worth checking whether 30A is actually your bottleneck. On my shepherd's hut build I ran the 18A isolated unit initially — perfectly adequate for a 100Ah lithium bank where I wasn't doing long drives anyway.

One thing nobody seems to mention: the isolated vs non-isolated decision matters more than the amperage for most setups. If your starter and leisure banks share a negative (common on narrowboats), non-isolated saves money and works fine. Different negative circuits — go isolated, no question.

Also factor in that the Orion needs proper input voltage to do its job. Weak alternator output under load can throttle it significantly. Worth logging your actual alternator voltage with a multimeter before committing to a charger spec.

@VanNicola this is timely — I've been going back and forth on exactly this for my narrowboat. Currently running a split charge relay into a 200Ah Fogstar lithium bank and it's clearly not keeping up on longer cruising days.

Quick question though — did you notice any difference in engine running time needed to hit a decent state of charge? That's my main concern. The relay setup feels like I'm running the engine forever just to get from 50% back up to 80%.

Also wondering whether the Orion-Tr Smart plays nicely with a Victron BMV-712 for monitoring — anyone got both running together? Assuming the VE.Smart networking handles it but not 100% sure how the two talk to each other in practice.

@PaddyDixon split charge relays are fine until you've got lithium in the mix — then they become a proper liability. The relay doesn't know or care that your BMS is about to disconnect, so you get those lovely voltage spikes back into the alternator.

I ran a Victron Orion-Tr Smart 30A for about six months before upgrading to the 50A isolated version. The isolation is the bit people overlook — on a narrowboat your engine negative and domestic negative should ideally be kept separate anyway, and the isolated Orion enforces that properly.

One thing nobody mentions: the Bluetooth monitoring via VictronConnect is genuinely useful when you're trying to figure out why your bank isn't topping up on a long cruise. You can see exactly what charge stage it's sitting in rather than just guessing.