Swapped out my split charge relay for a Victron BMS — was it worth it?

After two seasons running a basic split charge relay setup in my Transit-based camper, I finally took the plunge last month and upgraded to a Victron SmartShunt 500A paired with a Cyrix-Li-Ct intelligent relay to manage my 200Ah lithium leisure battery properly. The old relay setup was fine when I had AGM, but once I switched to lithium it felt like flying blind — no real idea of state of charge, and I was a bit worried about overcharging through the alternator on long runs.

The install wasn't too painful. I already had a 40A DC-DC charger (Renogy unit) in place, so the SmartShunt slotted in on the negative side of the battery bank fairly neatly. I've got it talking to the Victron app via Bluetooth and the SoC readings have been rock solid — way more confidence than the old voltage-based guesswork. First proper trip was a week in the Cairngorms in October, and I managed to keep on top of usage much better than before.

Cost came to around £180 all in for the SmartShunt and the Cyrix relay. Not nothing, but honestly I wish I'd done it when I first fitted the lithium rather than bodging along with the relay.

Has anyone else made a similar jump? Curious whether others have found the SmartShunt readings stay accurate over time, or whether you need to do regular full-charge resets to keep it honest. Also wondering if anyone's integrated theirs with a Raspberry Pi or similar for logging — seems like it might be doable over Bluetooth.

MeadowCarl | 847 posts | ⭐ Regular Contributor

@HelenMoore great move! The SmartShunt genuinely transforms how you understand your system — going from guesswork to actual state-of-charge percentages is a bit of a revelation, isn't it?

One thing worth mentioning that people often overlook: make sure your Bluetooth history data is syncing properly with VictronConnect, particularly the discharge cycles counter. It's brilliant for spotting patterns over time, especially if you're wild camping and relying heavily on solar.

Also, did you pair it with a BMV-712 display or are you purely going phone-based? I found having a physical display mounted somewhere visible made a big practical difference day-to-day rather than constantly unlocking my phone.

What lithium batteries are you running alongside it? The Cyrix-Li-Ct really earns its keep when the BMS starts communicating properly with the alternator charging side. Curious how your setup responded first time out.

OldSparky52 | 2,341 posts | ⭐⭐ Senior Member

@HelenMoore the Cyrix-Li-Ct is doing the heavy lifting there — that voltage-sensing logic properly protects your lithium cells from merge-charging when the starter battery's already depleted. Worth understanding exactly what your Cyrix engagement/disengagement thresholds are set to, because the defaults sometimes need adjusting depending on your alternator's charge profile.

One thing nobody mentions: pair the SmartShunt data with Victron Connect's historical discharge graphs after a few weeks. You'll start spotting patterns — parasitic draws you never knew existed, inefficient inverter loads, the lot.

The split charge relay was essentially flying blind. What you've got now is proper telemetry. If you're running Fogstar Drift cells specifically, also check whether your Cyrix thresholds align with their recommended charge voltage — some folk find the factory defaults sit slightly low for 100Ah lithium builds.

LochSpirit | 1,204 posts | ⭐⭐ Senior Member

Worth adding — the real game-changer with the Cyrix-Li-Ct isn't just voltage-based switching, it's the BMS integration allowing the battery to disconnect the alternator during a fault condition. A dumb split-charge relay cannot do that, and with lithium cells that's genuinely important for longevity.

@HelenMoore one thing to verify: what alternator are you running? Older Transit units with externally-regulated alternators can sometimes struggle when lithium drops the load suddenly. I ran into exactly this on my garden office's backup Transit donor vehicle — fitted a Victron Orion-Tr Smart DC-DC charger as an isolation layer between alternator and lithium bank, which resolved the voltage spike concern entirely.

The SmartShunt data via Bluetooth is addictive once you start watching it — state of charge accuracy after a proper capacity calibration cycle is noticeably better than any shunt I've used previously.