How to size, choose, and set up a portable generator that starts your tools cleanly and charges your batteries safely.
A portable generator only earns its keep if it starts your tools cleanly, holds voltage under load, and charges your batteries without damaging the electronics inside them. Get the sizing wrong, and you will trip the unit every time the compressor cuts in, or slowly cook a smart charger that was never built for rough power.
This guide explains how power tools and battery chargers draw current, how to size a generator for real work rather than the number on the box, and which models suit camping, trade sites, and home backup. The team at Outbax sells to Australian tradies, campers, and homeowners every day, so the advice reflects the loads people genuinely run.
Why Power Quality Matters More Than Raw Wattage
Two generators can carry the same wattage sticker and behave completely differently once you plug in a drill or charger. The difference is power quality, and it decides whether your gear runs happily or fails early.
Pure Sine Wave Power and Your Battery Chargers
Modern battery chargers, laptops, phones, and the battery management systems inside lithium packs all expect clean, smooth power that mirrors the mains. Inverter generators produce pure sine wave output, usually with total harmonic distortion below 3 per cent, which is close to what comes out of a household socket. Cheaper open-frame generators can deliver a rougher waveform that makes smart chargers run hot, throttle their charge rate, or fault out. For tool batteries, camera gear, or anything with a circuit board, a pure sine wave inverter generator is the safe choice.
Gentrax GT800 Pro Inverter Generator
Start-Up Current and Surge Watts
Almost every tool draws far more power in the first fraction of a second than it does while running. That spike is the start-up current, and it trips undersized generators. A tool rated at 1,200 running watts can demand 2,000 watts or more the instant you pull the trigger. Induction motors in compressors and pumps are the worst offenders, pulling three to seven times their running figure. Always size for the surge, not the steady state.
Brushless and Brushed Motors
Motor design shapes the demand too. Brushless tools use electronic controllers that draw current more efficiently and often surge less than older brushed motors, so they are kinder to a generator, though their electronics prefer clean power. Brushed motors tolerate rough waveforms better but pull higher current and waste more of it as heat.
How to Size a Portable Generator for Power Tools
Sizing is where most buyers go wrong. The trick is to separate the number you start with from the number you run at, then leave room to spare.
Starting Watts Versus Running Watts
Every generator lists two figures. Running watts, sometimes called rated watts, is what it delivers continuously. Starting watts, or maximum watts, is the brief peak it supplies to cover surges. A unit sold as 4.2kW max and 3.5kW rated gives you 3,500 watts all day and roughly 4,200 watts for the split second a motor spins up. Match your continuous load to the rated figure and your biggest surge to the maximum.
Adding Up Your Loads and Leaving Headroom
List every tool you might run at once. Add their running watts for the continuous total, then add the single largest start-up current, since tools rarely start at the same instant. As a rule, keep your steady load near 75 to 80 per cent of the rated output. That headroom protects the alternator and extends service life. A circular saw at 1,800 running watts, a work light at 100 watts and a charger at 200 watts sit comfortably on a 3.5kW rated unit, with room for the saw to surge.
VoltX VX3850 Pro 2-Wire Inverter Generator
Compressors, Pumps, and Other High-Draw Loads
Air compressors, water pumps, and anything with a capacitor-start motor deserve extra caution. Their inrush can be several times the running figure, and they cycle on and off unpredictably. If a compressor is central to your work, size up rather than hoping the surge rating copes. Kilowatts and kVA also differ. Generators are often rated in kVA, and real usable watts are roughly the kVA figure multiplied by a power factor of about 0.8, so a 3.5kVA unit delivers close to 2,800 working watts.
Matching the Generator to the Job
The right generator depends on where you work and what you run. Three broad use cases cover most Australian buyers.
Camping, Caravans, and RV Power
For campsites and caravans, quiet running and clean power matter most. You are charging phones, running a fridge, topping up a battery bank, and perhaps a coffee machine. A model like the Gentrax GTX4200 Inverter Generator handles those loads while staying friendly enough for a crowded campground, and its clean output keeps sensitive electronics and chargers safe.
» MORE: Compare quiet options in the Outbax inverter generators range
Here’s what one of our customers said about the Gentrax GTX4200 Pro Inverter Generator:
“Amazing unit, was surprised how economical it was and covered all our camp out needs. Best 2026 purchase thus far.”
Trade and Job Site Work
On site, you need dependable starts and enough grunt for saws, grinders and the occasional compressor. The Outbax GTX3500 Inverter Generator with Remote Electric Start earns its place here, letting you start it without walking back to the unit. Clean power also protects the chargers, keeping your cordless batteries topped up.
Here’s what one of our customers said about the Gentrax GTX3500 Inverter Generator:
“Purchased this generator and it’s great. Easy to start, quiet and the remote is great. Would suggest that the manual points people to connect the battery, apart from that …. It’s great.”
Home Backup During Outages
When storms knock out the grid, a larger unit keeps the essentials running. The Gentrax GS2-7500IE Inverter Generator suits home backup, carrying a fridge, lights, a few power tools, and phone chargers at once. For homes that only need to protect a computer or modem through short interruptions, a UPS from the Outbax power solutions range bridges the gap silently.
Setting Up and Running a Generator Safely on Site
Good sizing is wasted if the setup bleeds voltage or creates a hazard. A few habits keep your tools and chargers happy.
Gentrax GT1200 Inverter Generator
Lead Length and Voltage Drop
A long, thin extension leads to voltage drop before it ever reaches your tool. The further the run and the smaller the cable, the more voltage you lose, which makes motors run hot and chargers behave oddly. Keep leads as short as practical, use heavy-duty cable rated for the current, and always fully uncoil a lead, since a coiled lead traps heat.
Placement, Ventilation, and 240V Safety
Run the generator outdoors on level ground, well clear of doors and windows, and never inside a shed, tent, or garage, because exhaust fumes are deadly. Australian generators supply 240V single-phase power through standard 10-amp or 15-amp outlets, and a residual current device adds a vital layer of protection. Let the engine warm briefly before you load it heavily.
Managing Load and Run Time Across the Day
Generators are built to run at a sensible fraction of their rating, not flat out for hours. Inverter models with an economy mode throttle the engine down when demand drops, saving fuel and noise. Think about your duty cycle across a workday, plan your fuel stops, and give the unit lighter spells rather than holding it near maximum. A silent inverter generator that idles between bursts of work is easier on the machine and your ears.
Choosing the Right Generator for Tools and Chargers
Once you know your loads, the decision comes down to capacity, power quality, and noise.
Gentrax GTX6600 Inverter Generator
Picking Capacity for Your Tools
For light camping and charging, around 2 to 3kW is plenty. For general trade work with saws and a small compressor, 3.5kW rated is the sweet spot, which is why the Outbax Gentrax GT3500 Inverter Generator is such a popular pick. For home backup or heavier tools running together, step up to a 7kW class unit.
When Clean and Quiet Is Worth Paying For
An inverter generator costs more than a basic open-frame model, but its clean, pure sine wave power protects your chargers, and the lower noise keeps you welcome on campgrounds and residential streets. If your work depends on cordless batteries and sensitive electronics, that premium pays for itself. For fully silent charging away from mains power, a portable power station from the Outbax range pairs well with a generator, storing energy quietly and topping up when the engine runs.
» MORE: Browse capacities in the Outbax portable generators range
Getting Reliable Power for Every Tool and Charger
Choosing the right portable generator comes down to three things: size for the surge rather than the sticker, pick pure sine wave power if you charge batteries or run electronics, and set it up so long leads and poor placement do not rob you of voltage. Get those right, and one generator will cover camping trips, job sites and the next blackout without complaint. When you are ready to match a model to your loads, the Outbax portable generators range is the place to start.
