You buy a UPS with 1000VA printed on the box, expecting it to keep your PC and router alive for half an hour, then the power cuts and everything shuts down in seven minutes. The fault usually lies not with the unit but with the fact that the printed number describes the capacity it can carry, not the duration it can hold out. This guide breaks the formula down so you can work it out yourself before buying.
The formula: from amp-hours to minutes
Backup time is a division: the energy stored in the batteries divided by how fast the load draws it. A battery is rated in amp-hours at a given voltage, while a load is measured in watts. To bring both into one unit, multiply battery voltage by capacity. Example: two 12V 7Ah batteries in series give 24V × 7 = 168 watt-hours on paper.
But not all of that energy reaches your equipment. Sealed lead-acid batteries should never be drained to empty, because repeated deep discharge sharply shortens their life, so about half the capacity counts in practice. And the inverter that steps voltage up to 220V loses part of it as heat, at a typical efficiency near 85%. That leaves roughly 71 watt-hours available.
The last step: minutes equal the available energy divided by the load in watts, multiplied by 60. At a 150W load that gives about 28 minutes on paper. Subtract a quarter as a safety margin, because a battery under fast discharge delivers less than its printed rating and because performance falls off with age and heat, which leaves a realistic figure near 20 minutes.
What to know before doing the math
- Your real load in watts: do not add up what is printed on power supplies, since that states the maximum rather than actual draw.
- VA versus watts: the rating in watts is lower, calculated by multiplying the VA figure by the power factor — around 0.6 on many units and 0.9 on newer ones.
- Battery count and capacity: a unit with two 12V 9Ah batteries stores twice the energy of one with a single comparable battery, even if the VA figures match.
- Load percentage: the closer the load sits to the maximum, the more disproportionately runtime shrinks, and loading to half capacity extends battery life.
- Heat and dust: lead-acid batteries perform best near 25 degrees Celsius, so in an Iraqi summer place the unit somewhere shaded and well ventilated.
Long backup for a tiny load: Mini UPS GeTX GSP2
If what matters is keeping the router and fibre unit alive during an outage rather than the PC, the formula swings in your favour. This is a direct DC unit with 9V and 12V outputs and a PoE output at 15V and 24V, rated 36W. Because it never converts to 220V it avoids the conversion loss, so runtime here is measured in hours rather than minutes.
One battery, a shutdown window: UPS GeTX GXK-850-C
A Line interactive unit rated 850VA with an LCD screen, running on a single 12V 9Ah battery. That is 108 watt-hours on paper, of which about 46 stay usable: enough minutes to save your work and shut down cleanly, not to keep working. The screen shows load percentage, the fastest way to tell whether you are past its rating.
Two 7Ah batteries: UPS GeTX GXK-1000-C
1000VA, Line interactive, LCD screen and two 12V 7Ah batteries — 168 watt-hours on paper and about 71 available. Note the key detail: the VA figure is higher than the unit above, yet two 7Ah batteries together deliver only a moderate gain over a single 9Ah one. The number tells you what you can plug in, not how long it runs.
The real jump in runtime: UPS GeTX GXK-1500-C
1500VA, Line interactive, LCD screen and two 12V 9Ah batteries — 216 watt-hours on paper and about 92 available. At a 100W load, meaning a modest desktop with a monitor and router, the math gives roughly 55 minutes on paper and about 40 in practice. This is where a UPS becomes genuine backup rather than a shutdown window.
Higher rating, same battery: UPS GeTX GXK-2000-C
Here is the clearest lesson in this guide. This unit is rated 2000VA, higher than the one above, yet it runs on two 12V 9Ah batteries — the very same battery bank. It carries more devices, but on the same load it will not give meaningfully more minutes. Choose it when your concern is the number of devices, not the length of the runtime.
Same rating, bigger battery: UPS Gaming GeTX GTXF-2000
And here is the flip side of that lesson: also 2000VA, also Line interactive, but with two 12V 12Ah batteries. That totals 288 watt-hours against 216, close to a third more at the same rating, which translates into a proportionally longer runtime. Between two units with matching VA figures, the real comparison lives in the battery line.
Online class for sensitive gear: UPS APC Easy Online SRV 1000VA
Online units use double conversion: power always passes through the unit and comes out clean and steady, with no transfer time at the moment of a cut. A logical choice for anything that cannot tolerate fluctuation, such as a small server or a core network device. But Online does not mean longer backup; its advantage is output quality, while duration stays governed by the batteries.
An expanded battery bank: UPS GeTX Online GXT-2000-CON
2000VA in the Online class with high-frequency design and an LCD screen, paired with six 12V 7Ah batteries. Total stored energy is 504 watt-hours on paper, more than double any unit before it here, which suits an office or network room needing real continuity. Ventilation at this size is a requirement, not a luxury.
Common mistakes that cut your backup time
- Plugging in a laser printer: its fuser draws a huge momentary current that can trip the unit instantly, so it belongs on the wall socket.
- Plugging in an air conditioner, fridge or heater: these are heavy loads outside the range of a desktop UPS, and running them ends in a shutdown or damage.
- Trusting the VA number alone: as the 1500 and 2000 examples showed, that number describes capacity rather than time.
- Leaving the unit unplugged for weeks: a lead-acid battery is damaged by sitting empty, so recharge it periodically if you are storing the unit.
- Keeping it somewhere enclosed or dusty: trapped heat quietly eats battery life, and dust blocks the ventilation slots.
- Ignoring the replace-battery warning: when runtime drops noticeably the answer is a new battery, not a new unit.
Frequently asked questions
How long does a 1000VA UPS last?
There is no single answer, because duration depends on its battery and your load. A unit with two 12V 7Ah batteries has about 71 watt-hours available, meaning close to 20 minutes at a 150W load and under ten minutes at 300W.
Does a higher VA rating mean longer backup?
Not necessarily. The figure sets the maximum load the unit can carry, while duration is set by the batteries alone. This list has a 1500 and a 2000 sharing an identical battery bank, so they run roughly the same time at the same load.
Can I run a fridge or air conditioner on a UPS?
No. Desktop UPS units are designed for light electronic loads: a computer, monitor, router and cameras. An air conditioner, fridge or heater draws a high momentary current that trips or damages the unit, and those loads call for an inverter with a large battery bank.
How long will my router stay up in a power cut?
Far longer than anything else, because it is one of the smallest loads in the house. On a UPS shared with a computer you get minutes, but give the router a small dedicated DC unit and the time is measured in hours.
How long does a UPS battery last and when should I replace it?
Sealed lead-acid batteries are consumables that lose capacity gradually, and the loss accelerates with heat and frequent discharge cycles. The practical signal is runtime dropping noticeably, or the unit raising a replace warning. At that point you usually replace the battery alone.
What is the difference between Line interactive and Online in backup time?
No fundamental difference in duration, since it comes from the batteries either way. The difference is output quality: an Online unit delivers clean, steady voltage with no transfer time, while Line interactive is cheaper and better suited to home and office use.
Does leaving a UPS plugged in all the time harm it?
No, that is its normal state: the unit charges the battery and holds it ready on standby. The harm comes from the opposite, leaving it unplugged for weeks until the battery self-discharges flat. If you store it for long, charge it every few months.
Practical takeaway
Start from your load, not the number on the box. The quick rule: multiply battery voltage by amp-hour capacity by the number of batteries, take about 40% of the result, then divide by your load in watts and multiply by 60. For the internet alone a small DC unit is enough, and for a whole office look for an expanded battery bank rather than a bigger figure. Every unit here is available with delivery to all Iraqi governorates and cash on delivery.
