Computer UPS from Inverter and Lithium Rack Battery

Has anyone actually managed to get a clean UPS-style setup working for a laptop or desktop using a proper inverter and lithium rack battery? I'm trying to work out if this is feasible for my shepherd's hut where I run a small home office setup.

My concern is the switchover time when grid input drops — most computer PSUs seem tolerant of brief gaps but I've read that some sensitive equipment doesn't like it. Is there a meaningful difference between a Victron Multiplus (with its near-zero transfer time) versus something cheaper like a Growatt hybrid?

A few specific questions I'm wrestling with:

• Does the BMS cutting out under load cause any issues downstream for the inverter's transfer relay?
• Would a 48V rack battery (looking at Fogstar or similar) be overkill for a small office load, or is that just the sensible way to build it?
• Anyone using this setup with a NAS as well as a workstation?

I'm currently running a basic Renogy 12V setup in the cabin but want to step up properly for the hut office build. The idea of having genuine UPS protection rather than just "the lights stay on" feels like it'd be worth the investment if the switchover time is actually reliable enough for computing loads.

What are people actually running day-to-day? Real-world experience would be more useful than spec sheets right now.

Running my narrowboat essentially as a floating UPS for three years now — the whole boat is on a Victron Multiplus so my laptop never even blinks when the engine cuts out.

The key thing @SolarDoug is the transfer time. Most inverter/charger combos aren't true online UPS — there's a 20ms switchover gap. Modern laptops handle that fine, but some older desktops with fussier PSUs will reboot.

What I found works brilliantly:

• Victron Multiplus (any size)
• Fogstar Drift lithium as your buffer bank
• VE.Bus configured so grid/shore power charges, inverter runs loads constantly

The Multiplus in "inverter first" mode means your computer genuinely never sees a transition. Been solid through countless marinas losing power without a single dropped connection call.

What's your shepherd's hut running for loads — just a laptop or proper desktop workstation?

@SolarDoug yes absolutely doable! I've got a similar setup in my garden office — Victron MultiPlus-II feeding the whole room, so my desktop never even notices a grid blip. Feels like proper UPS behaviour once everything's dialled in.

Key thing is the transfer time — the MultiPlus switches in under 20ms which most computers handle fine. Older ATX PSUs can be fussier though so worth checking.

I'm using a Fogstar Drift 48V rack battery and it's been rock solid. The Victron ESS assistant is the bit that makes it behave like a UPS properly rather than just an inverter sitting there.

@LisaKelly66 curious what you're running on yours — do you get any issues with sensitive electronics or has it just worked?

@SolarDoug the elephant in the room nobody's mentioned yet — your computer doesn't care why the power's clean, just that it is.

Ran into this exact rabbit hole on the boat. Spent three weeks agonising over transfer times, only to discover my ancient Dell laptop had been cheerfully running off a dodgy inverter the whole time anyway because

@PanelKate snap — garden office here too. One thing worth adding: the transfer time is the bit that catches people out. Most "proper" UPS-style inverters like the Victron Multiplus claim sub-20ms switchover but I've found some cheaper pure sine units are way slower in practice.

For a desktop you really want sub-20ms or the PSU will dip and reboot. Laptops are more forgiving because the internal battery buffers it anyway.

My setup uses a Multiplus-II 24/3000 with Fogstar Drift 24v batteries and honestly the desktop hasn't flickered once in 18 months — mains dropout is completely invisible to the machine.

If budget's tight, even a decent APC UPS between the inverter output and your computer adds a proper zero-transfer layer as a belt-and-braces. Bit belt-and-braces but it works.

@Dizzy70 nailed the transfer time thing — worth knowing the MultiPlus-II is around 20ms which most modern PSUs handle fine, but some cheaper desktop units absolutely don't. Had grief with an old Dell in my shepherd's hut before I realised.

One thing nobody's flagged yet — your BMS matters here as much as the inverter. If the BMS disconnects under load (cell imbalance, low temp, whatever) you get a hard cut regardless of what Victron kit you've got upstream. Fogstar or a decent rack battery with a solid BMS is worth the extra.

Also worth enabling the PowerAssist feature if you go MultiPlus route — helps smooth things out considerably.