Smartshunt Installation on Campervan Starter / Engine Battery

Been scratching my head over this one for a while now and can't seem to find a straight answer anywhere.

I want to fit a Victron SmartShunt to my starter battery (separate from the leisure bank which already has one). The van has a split-charge relay setup and I'm trying to get proper visibility on what the engine battery is actually doing — mainly whether the alternator is charging it correctly and keeping tabs on parasitic drain when parked up for extended periods.

The bit I'm stuck on is shunt placement. From what I understand, the shunt needs to go on the negative side and all negative loads/returns must pass through it to get accurate readings. That's straightforward enough on a leisure battery with a clean dedicated negative. But on the starter battery you've got:

• Engine earth straps going to the chassis
• Chassis used as a return path for half the van's 12v circuits
• Potentially the split-charge relay negative as well

Does anyone actually have this wired up cleanly in practice? Do you end up having to re-route chassis earths to go through the shunt, or is there a smarter way to handle it? Feels like it could get messy very quickly on a factory wiring setup.

Running a Fogstar lithium leisure bank on a separate circuit so I'm not trying to combine the two shunts — just want standalone monitoring on the starter side.

Anyone tackled this on a camper conversion with original vehicle wiring still largely intact? Would be good to hear what actually worked rather than the theoretical ideal.

@Mike1980 fitting a SmartShunt to a starter battery is a bit like putting a Fitbit on a marathon runner who only ever sprints to the fridge — technically works, but you'll mostly be watching a battery that's perpetually at 100% going "yep, still full, still full, oh wait the engine started, back to full"

@MoorLee's analogy is pretty spot on actually.

Ran into this exact situation with my tiny house build — I monitor my leisure bank obsessively with a SmartShunt, but the starter battery just gets a simple voltage alarm wired to the Victron Cerbo.

The starter battery's job is one massive burst then immediate recharge from the alternator. The SmartShunt's coulomb counting is designed for batteries that cycle — tracking charge in and out over time. A starter battery rarely does that in any meaningful sense, so your SOC reading will be almost permanently sat at 98-100% and telling you precisely nothing useful.

If you're genuinely worried about starter battery health, a battery conductance tester (Midtronics do decent ones) will give you far more actionable data than any shunt ever could.

Save the SmartShunt budget for your leisure bank where it'll actually earn its keep.

@Mike1980 worth being clear about why you want to monitor the starter battery specifically — that changes the answer considerably.

On my narrowboat I run a SmartShunt on the starter battery purely to catch a failing alternator early, not for SoC tracking. For that use-case it's absolutely worthwhile — you're watching voltage under load and charging voltage, not cycle depth.

If you're going down this route, make sure your shunt is sized correctly. Starter motors can pull 200–400A+ during cranking, so don't cheap out on the shunt rating. Victron's 500A unit is the sensible choice here.

One gotcha people miss: the SmartShunt needs a permanent negative connection from the battery, not via the vehicle chassis. Engine bays with poor earthing will give you garbage readings. Run a dedicated negative cable back to the battery terminal.

On my narrowboat the starter battery just... starts the engine and then immediately gets topped up by the alternator, so the SmartShunt would basically just read "fine, fine, fine, oh — fine again" on a loop.

@FenlandSolar makes a fair point actually — why do you need it monitored?

On my motorhome I just fitted a simple voltage alarm on the starter battery rather than a full SmartShunt. Does the job — alerts me if it drops below threshold overnight. Shunt felt like overkill for something that's either charged or it isn't.

If you're dead set on the SmartShunt though, the wiring's straightforward — negative cable from starter battery through the shunt, that's it. Just make sure your negative busbar setup is sorted first or you'll get dodgy readings.

Worth knowing Victron's own docs say the SmartShunt works fine on starter batteries, it just depends what data you actually want from it.