Battery Back Up Guide
This guide explains what your inverter and battery system can support during a power outage, particularly during major weather events such as cyclones and floods, which are common in Australia.
When planning for back-up power, it’s important to understand two key factors:
- Amp Capacity (Peak Load)
This is the maximum instantaneous load your inverter can handle.
Spikes occur when appliances with compressors or heating elements turn on (e.g., fridges, freezers, kettles, toasters).
If your combined load exceeds the inverter’s amp rating, the system will trip. (FYI: Hinen inverters will usually automatically restart within 3 to 5 mins).
- kWh Consumption (Average Load per Hour)
This is the energy you use each hour, which determines how long your battery will last.
Higher continuous loads = shorter back-up duration
How Easily Loads Can Spike
A standard:
- 5 kW inverter supports up to 22 amps
- 10 kW inverter supports up to 45 amps
Below is an example of how quickly loads can add up.
| Load | Spikes (amps) | Ave Standing Load (Watts) |
| Kettle | 10 | 300 |
| Toaster | 5 | 200 |
| Air Fryer | 7 | 800 |
| Washing Machine | 4 | 800 |
| Dishwasher | 6 | 1200 |
| Fridge x 2 | 6 | 600 |
| Freezer | 5 | 300 |
| Lights | 1 | 250 |
| Fans | 1 | 300 |
| TV’s | 1 | 250 |
| Pool Pump | 5 | 1200 |
| Bedroom A/C | 10 | 800 |
| Total | 61 A | 7000 (7KW) |
Essential Loads Only
When we connect your back-up circuits to the battery, we recommend limiting the loads to essential appliances only.
With a 5 kW inverter, avoid turning on the kettle and toaster at the same time, as this may exceed capacity.
Recommended Essential Loads:
| Essentials | Spikes (amps) | Running Load (Watts) |
| Kettle | 10 | 300 |
| Toaster | 5 | 200 |
| Fridge x 2 | 6 | 600 |
| Freezer | 5 | 300 |
| Lights | 1 | 250 |
| Fans | 1.25 | 300 |
| TV’s | 1.25 | 300 |
| Total | 29.5 A | 2250 (2.25KW) |
Battery Runtime Guide – Essential Loads
Assuming:
- Worst-case weather (2 days of rain / no solar)
- Approx. 2 kWh per hour usage
- Zero solar contribution
Even on cloudy days, short bursts of sun will help recharge your battery.
With careful management, a good-sized storage system can run off grid for days.
| Inverter | Capacity (Amps) | KWh Usage | KWH Storage | Hours |
| 5 | 22 | 2 | 15 | 7.5 |
| 5 | 22 | 2 | 20 | 10 |
| 5 | 22 | 2 | 25 | 12.5 |
| 5 | 22 | 2 | 30 | 15 |
| 5 | 22 | 2 | 35 | 17.5 |
| 5 | 22 | 2 | 40 | 20 |
| 5 | 22 | 2 | 45 | 22.5 |
| 5 | 22 | 2 | 50 | 25 |
| 10 | 45 | 2 | 15 | 7.5 |
| 10 | 45 | 2 | 20 | 10 |
| 10 | 45 | 2 | 25 | 12.5 |
| 10 | 45 | 2 | 30 | 15 |
| 10 | 45 | 2 | 35 | 17.5 |
| 10 | 45 | 2 | 40 | 20 |
| 10 | 45 | 2 | 45 | 22.5 |
| 10 | 45 | 2 | 50 | 25 |
Air Conditioning During Back-Up
We know that sleeping with air conditioning is important in hot summer nights.
However, we do not recommend connecting A/C units to back-up circuits due to:
- High amp spikes when compressors start
- High hourly consumption
- High risk of tripping a 5 kW inverter
- Rapid depletion of battery storage
Below shows what happens if A/C is used during a blackout.
10 kW Inverter (45 A capacity).
Assuming 4 kWh per hour usage with A/C running.
| Inverter | Capacity (Amps) | KWH Usage | KWH Storage | Hours |
| 10 | 45 | 4 | 15 | 4 |
| 10 | 45 | 4 | 20 | 5 |
| 10 | 45 | 4 | 25 | 6 |
| 10 | 45 | 4 | 30 | 8 |
| 10 | 45 | 4 | 35 | 9 |
| 10 | 45 | 4 | 40 | 10 |
| 10 | 45 | 4 | 45 | 11 |
| 10 | 45 | 4 | 50 | 13 |
Even with 40 kWh of storage, running A/C overnight would drain the battery in around 10 hours. It may be fine if the following day is sunny, but in poor weather it becomes risky.
For this reason, we strongly recommend excluding A/C circuits from the back-up system.
Founder of Horan & Bird. Director of Master Electricians Australia and Board Member of Solar Accreditation Australia. John has played a key entrepreneurial role in the transformation of the Energy Landscape in Queensland.
