Will my fibre survive loadshedding?

The uncomfortable catch: your house isn’t the only thing that needs power

You can keep your own equipment running indefinitely and still lose internet. Fibre is passive between your home and the exchange, but the active equipment in between — street cabinets, aggregation points, the operator’s exchange gear — needs power too. Most networks run batteries on that kit, but batteries degrade and repeated deep cycles mean some cabinets don’t recover until they’ve recharged.

So a UPS at home solves your half of the problem, which is usually the half that fails first. If your connection dies at the same time every day even with a UPS running, the fault is upstream and no amount of battery will fix it. Our uptime monitor timestamps every dropout, which tells you which half you’re dealing with.

How much power does fibre equipment actually use?

Very little, which is what makes this worth doing. Typical figures:

For a firmer number, check the label on each power brick — it lists output volts and amps, and volts × amps gives you watts. That’s the brick’s maximum, so actual draw is usually lower, which makes it a safely pessimistic input. Higher-end XGS-PON units and gaming routers with multiple radios sit at the top of these ranges or above.

Methodology — and why “usable” is less than the label

The calculation is deliberately simple:

Runtime = (rated Wh × usable depth-of-discharge × conversion efficiency) ÷ total watts

• Depth of discharge. Lead-acid and AGM batteries are conventionally sized to use only about 50% of rated capacity — going deeper repeatedly shortens their life sharply. LiFePO4 tolerates roughly 80%. This is the single biggest reason a “300 Wh” unit doesn’t give you 300 Wh.
• Conversion efficiency. Turning DC battery power into 230 V AC and back into DC for your router wastes energy twice; inverters typically run 85–95%. A DC mini-UPS that feeds 12 V straight to the router skips a conversion and lands nearer 95% — which is why those small units often outlast a bigger AC UPS on the same nominal capacity.
• Not modelled: battery ageing (an old battery can be at half its rated capacity), temperature, self-discharge, and the UPS’s own idle consumption. At the very low loads here, some AC UPS units spend a noticeable share of the battery just running themselves.

Because of that last point, treat the result as an optimistic ceiling for a healthy battery, and size up if the runtime matters to you.

What size should you buy?

Put your target hours into the calculator and it works backwards. As a rough sense of scale, an ONT plus router at ~18 W on a lead-acid unit needs roughly 40 Wh of rated capacity per hour of runtime; on LiFePO4, closer to 24 Wh. That’s why small lithium units punch well above their labelled size.

Two practical notes. Put the ONT and the router on the backup — powering only one leaves you with no connection either way. And if you’re on fixed wireless rather than fibre, none of this helps when the tower itself is down; see why is my internet slow for how to tell the difference.