Anyone else running two completely separate 12v systems in the same build?

Just finishing off my shepherd's hut and I've ended up with what I can only describe as two totally independent 12v setups — one for the main living stuff (lights, 12v sockets, diesel heater) running off a 200Ah Fogstar Drift LiFePO4, and a separate smaller 100Ah AGM purely for the security camera and a bit of comms gear that needs to stay live even if the main bank is switched off or in storage.

The two systems aren't linked at all right now — different solar inputs, different charge controllers. The main bank has a Victron SmartSolar MPPT 100/20 and about 400W of panels on the roof. The AGM side is just a cheap Renogy 10A PWM with a single 100W panel tucked round the side. It's a bit of a bodge if I'm honest, but it works.

What I'm not sure about is whether there's a neater way to handle this — maybe a Victron Battery Protect or a DC-DC charger to let the main bank top up the AGM when it's got surplus? Or is keeping them totally isolated actually the smarter approach for a security/standby circuit? Curious what others have done.

@PikeTom mate, I've been running exactly this on the boat for two years — main domestic bank and a completely separate starter/bow thruster setup that I've sworn at independently on at least four separate occasions.

The beautiful thing is when something goes wrong, you get to play "which system hates me today?" — it's like having two dogs, except both of them

@PikeTom two 12v systems in one build — so you've essentially reinvented the narrowboat, welcome to the club 🚢

@PikeTom I've got something similar going on with my garden office — main system handles the everyday loads and I kept EV trickle charging completely isolated from it after one too many incidents with voltage sag affecting sensitive kit.

Quick question though — how are you handling the physical battery separation? Are they in completely different enclosures or just electrically isolated in the same space? I'm also curious whether you're using any kind of battery-to-battery charger between the two banks (I've been looking at the Victron Orion-Tr Smart for exactly this kind of setup) or keeping them genuinely 100% independent with no crossover at all.

The redundancy angle appeals to me massively from an emergency backup perspective — if one bank or its associated wiring develops a fault, the other just carries on.