Anyone else using an old UPS as emergency backup for the router and NAS?

Been running an old APC Back-UPS 700VA under the desk for about three years now. Picked it up from a local IT surplus place for £8. Swapped the sealed lead-acid out for a fresh one from Tayna Batteries and it's been solid ever since.

The router, a small Netgear switch, and a Synology NAS sit behind it. During a grid outage last winter — we had a rough few weeks out here — it bridged the gap long enough for my Victron MultiPlus to spin up properly and take over. Without it, the NAS would have been mid-write on a backup job. Not ideal.

The only thing worth mentioning is that older UPS units can be deceptive about their runtime estimates. The software still reports based on the original battery spec, so you end up with wildly optimistic numbers until you recalibrate or just run it down yourself and clock it manually.

A few things I'd flag for anyone considering this route:

• Battery condition matters enormously — a tired cell will give you minutes, not the 20–30 you're expecting
• Pure sine wave vs. modified sine — some NAS units and certain networking gear are fussy about this
• Idle draw — even a modest UPS sips a few watts continuously, worth factoring in if you're already watching every amp

Curious whether anyone's gone further and integrated an old UPS into a proper off-grid setup rather than just using it as a bridging device. Feels like there's more potential there that most people ignore.

@EcoFlow_Master that's a cracking find for £8.

Quick question though — have you looked at swapping that SLA for a lithium cell instead? I've been eyeing up doing something similar for my garden office but wondering if the APC's charge profile would actually damage a LiFePO4 if you just dropped one in as a straight swap.

Also curious what runtime you're actually seeing on the router + NAS combo? Mine would need to cover a Synology DS223 and a mesh node, and I'm trying to figure out whether a UPS hack like this is worth it or whether I should just bite the bullet and wire something properly into my Victron MultiPlus setup for emergency backup.

The £8 price tag is doing a lot of heavy lifting in my decision making here, not gonna lie.

Really nice setup @EcoFlow_Master! I've got a similar arrangement with an older APC ES 550 keeping my router and a small NAS ticking over during outages.

One thing worth mentioning that I haven't seen come up yet — if you're running a NAS specifically, it's worth configuring the UPS communication via USB so the NAS can trigger a graceful shutdown automatically if the battery gets low. Most NAS operating systems like TrueNAS or even the Synapse DSM software support APC's protocol natively. Saved me from a corrupted array once when an outage lasted longer than expected.

Also seconding @DaiLewis69's curiosity about lithium — I've been tempted myself but the charge profile incompatibility with standard SLA chargers in these units always puts me off unless you're comfortable modifying the internals.

Great thread! I've got an old MGE Ellipse 650 doing similar duty — rescued it from a skip outside an office block about two years ago, just needed a new battery. One thing worth mentioning that I haven't seen covered yet: check your UPS's transfer time when mains drops out. Most older units switch over in around 4-8ms, which is absolutely fine for routers and NAS drives, but worth verifying if your NAS is particularly fussy about power interruptions. Also, @DaiLewis69 raises an interesting point about lithium — the main snag is that most of these older APC and MGE units charge at a fixed profile designed for SLA, so you'd need to be careful not to overcharge a lithium replacement without some sort of BMS protection built in. Swapping like-for-like SLA is honestly the path of least resistance for most people.

Been wondering about this for my shepherd's hut setup actually. Currently the router drops every time a cloud passes over and my Victron MPPT does its little recalibration dance.

Couple of questions though:

• What's the typical runtime you're getting on the swapped SLA? Curious whether it's actually worth the battery cost vs just tolerating the brief outages
• Has anyone tried wiring one of these into a proper off-grid system rather than running it purely as a standalone UPS? Feels like there should be a smarter way to keep the router on the same battery bank rather than having a separate little SLA sat under a desk doing nothing 90% of the time

@EcoFlow_Master did you have to do anything to the APC's internal charging circuit when you swapped the battery, or did it just accept the new SLA without complaint?