Understanding Battery Runtime
How long your battery backup lasts depends on two main factors: the capacity of your battery (measured in watt-hours or Wh) and how much power your appliances draw. Understanding this relationship helps you choose the right system for your needs.
The Basic Formula:
Runtime (hours) = Battery Capacity (Wh) / Power Draw (W)
For example, a 1000Wh battery powering a 100W load would last approximately 10 hours (accounting for efficiency losses, expect about 8-9 hours in practice).
What Affects Battery Runtime?
Battery Capacity
Measured in watt-hours (Wh). A 2000Wh battery holds twice as much energy as a 1000Wh battery. Larger capacity = longer runtime.
Power Draw
How much power your connected devices consume, measured in watts (W). A fridge uses about 100-150W when running, while an electric kettle might use 2000-3000W.
Inverter Efficiency
Converting DC battery power to AC household power loses about 10-15% efficiency. A 1000Wh battery delivers about 850-900Wh of usable power.
Cycling Behaviour
Appliances like fridges cycle on and off, so they don't draw continuous power. A fridge might only run 30-40% of the time, extending actual runtime significantly.
Real-World Runtime Examples
Here's how long common battery sizes will power typical household loads. These estimates account for efficiency losses and realistic usage patterns.
Fridge Only
A typical American fridge-freezer draws 100-150W when the compressor runs, but cycles on/off (running about 35% of the time on average).
| Battery Size | Estimated Runtime |
|---|---|
| 500Wh | 8-12 hours |
| 1000Wh | 16-24 hours |
| 2000Wh | 32-48 hours |
Fridge + Lights + Phone Charging
Adding LED lights (10-20W total) and phone/tablet charging (10-20W) to your fridge backup. This is a common "essentials" setup for outages.
| Battery Size | Estimated Runtime |
|---|---|
| 1000Wh | 10-16 hours |
| 1500Wh | 16-24 hours |
| 2000Wh | 20-32 hours |
Full Home Essentials
Running fridge, lights, TV, router, and occasional microwave use. This requires a larger system and careful load management.
| Battery Size | Estimated Runtime |
|---|---|
| 2000Wh | 4-8 hours |
| 3000Wh | 6-12 hours |
| 5000Wh+ | 10-20 hours |
How to Extend Your Battery Runtime
Prioritise essential loads
Only power what you truly need during an outage
Use LED lighting
LEDs use 80% less power than traditional bulbs
Turn off the fridge temporarily
A closed fridge stays cold for 4-6 hours
Add solar panels
Even small panels can extend runtime significantly
Get an expandable system
Many systems allow adding extra battery packs
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