Maintaining Fiat vehicle Battery via Solar

Interesting topic this — it's something I've been thinking about with my van conversion build.

The typical setup I've seen (and what I'm working towards) is using a DC-DC charger or a split-charge relay to manage the relationship between the leisure bank and the starter battery. But the balancer approach for maintenance charging is something I hadn't fully considered until recently.

My current setup runs a Victron SmartSolar MPPT 100/20 feeding a 200Ah Fogstar Drift LiFePO4 leisure battery. Once that bank is sitting at absorption/float, there's genuinely surplus energy available — and the Fiat's OEM battery just sits there doing nothing useful.

A few questions I'd throw out to the forum:

• Does anyone have experience with balancers specifically on Fiat Ducato chassis? The Ducato's smart alternator behaviour is already a headache for split-charge setups, so I'm wondering if a balancer introduces any complications with the BMS/ECU relationship.
• Is a dedicated VSR (Voltage Sensitive Relay) still a viable alternative, or are balancers genuinely worth the extra cost for a maintenance scenario rather than bulk charging?
• What voltage thresholds are people setting for triggering the feed across? I'd want to make sure the leisure LiFePO4 resting voltage doesn't confuse the relay logic — LiFePO4 sits high even at 50% SoC.

The core appeal here is obvious — keeping the starter battery conditioned over winter or during long storage periods without any manual intervention. That's a real practical win for van lifers who leave the vehicle parked for weeks.

Anyone running a similar arrangement who can share what's actually working in practice?

@WayneJames the classic van conversion rabbit hole — you start thinking "I'll just keep the starter battery topped up" and six months later you've got a Victron MPPT, a Fogstar lithium leisure bank, and you're explaining to your partner why the bathroom budget has mysteriously vanished 😄

Seriously though, a DC-DC char

@WayneJames done exactly this on my static — different context but same principle applies. The bit people miss is that a DC-DC charger (I run a Victron Orion-Tr Smart) isn't just about maintaining the starter battery, it's about protecting it. Standard split-charge relays will happily drag your starter battery down alongside your leisure bank if something goes wrong.

On a Fiat Ducato specifically, watch the intelligent alternator issue — the ECU plays games with voltage output and a dumb VSR will behave erratically. The Orion handles it properly.

Solar into the leisure bank, Orion keeping the starter topped up from there — clean, simple, works.

Worth flagging something specific to Fiat vehicles — the Ducato platform (which covers most van conversions) uses a smart alternator that deliberately varies its output voltage. This causes problems for split-charge relays, which rely on a stable voltage threshold to detect charging. You can end up with the relay chattering or simply not triggering properly.

A DC-DC charger (Victron Orion-Tr Smart is the go-to) handles this correctly — it'll accept the variable input and still deliver a proper charge profile to your leisure bank.

@BordersNomad makes a fair point about what people miss — I'd add that on the Ducato specifically, you also need to check whether your vehicle has the EFB or AGM starter battery, because that affects how sensitively the battery management system responds to parasitic loads from your leisure setup.

What year is your Fiat, @WayneJames?

Good shout from @ExFirefighter on the smart alternator point — that's caught a lot of people out. Just to add to that thread: if you're running a solar-to-starter battery setup on a Fiat Ducato platform, make sure your solar controller isn't trying to push voltage into the starter battery when the smart alternator is simultaneously doing its thing. The voltage sensing can get confused and you can end up with neither source charging properly.

What I'd suggest is isolating the solar input specifically for your leisure bank and letting the DC-DC charger handle the starter battery relationship entirely. Keeps things clean and avoids any weird interactions. Some of the Victron Orion-Tr Smart units handle this really well as they'll detect the alternator state properly.

What DC-DC charger are you looking at @WayneJames?