Quick answer: Divide your battery's usable capacity (kWh) by your actual running load (kW) to get runtime in hours. A 10.24kWh battery at 90% depth of discharge running a 1kW load lasts roughly 9 hours — but the real number depends entirely on what's switched on, not a single figure printed on the box.
Runtime is a moving target, not a fixed number
The most honest answer to "how long will my battery last?" is: it depends what you're running. A battery that lasts 14 hours powering lights, fans and a fridge might last 3 hours if an AC unit and a microwave are added to the mix. Runtime isn't a fixed spec — it's a calculation you can do yourself once you know two numbers.
The formula
Runtime (hours) = Usable battery capacity (kWh) ÷ Current load (kW)
Usable capacity = battery's rated kWh × depth of discharge (usually 85–90% for the LiFePO₄ batteries we install).
Worked examples, same battery, different loads
A 10.24kWh battery at 90% DoD gives roughly 9.2 kWh usable.
| Load running | Approx. draw | Estimated runtime |
|---|---|---|
| Lights + fridge + router | 0.3 kW | ≈30 hours |
| Above + TV + fans | 0.6 kW | ≈15 hours |
| Above + 1 AC unit (1HP) | 1.5 kW | ≈6 hours |
| Above + washing machine running | 2.0 kW | ≈4.6 hours |
This is why two households with an identical battery can report very different real-world backup times — the battery isn't underperforming, the load is simply different.
Solar recharge changes the picture during the day
The runtime calculation above assumes no solar input — the scenario during a night-time outage, for example. During daylight hours, solar generation offsets some or all of the load in real time, meaning the battery drains more slowly (or not at all, if solar output exceeds your current draw). This is why outages during the day are usually far less noticeable than overnight ones on a solar and battery system.
What actually shortens real-world runtime
Three factors quietly eat into the "textbook" runtime number:
- Inverter efficiency losses. No inverter is 100% efficient — typically 90–95% of stored energy actually reaches your appliances, with the rest lost as heat during conversion.
- Ambient temperature. Extreme heat can slightly reduce a battery's effective capacity and efficiency, though LiFePO₄ handles Nigerian conditions considerably better than lead-acid.
- Battery age. A battery nearing the end of its rated cycle life delivers somewhat less usable capacity than it did when new — a gradual decline, not a sudden drop.
How to extend runtime without buying a bigger battery
If runtime is shorter than you'd like, the cheapest fix is often behavioural, not hardware:
- Stagger heavy appliances. Running the washing machine and AC at different times, rather than together, meaningfully extends how long the battery lasts.
- Identify what's running that you didn't intend to. A second fridge in a store room or an always-on water heater is a common, invisible drain.
- Check your inverter's load-shedding priorities. Some hybrid inverters let you set non-essential circuits (like an outdoor light) to shut off first during extended backup.
When it's genuinely time for a bigger battery
If your realistic daily load consistently exceeds what your current battery can carry through your desired backup window, that's a sizing issue, not a usage issue — and it's a straightforward one to fix by adding capacity. This is exactly the calculation we run during a free energy assessment, using your actual appliances rather than averages.
FAQs
Does running the battery down to empty every day damage it?
Regularly discharging beyond the rated depth of discharge does shorten lifespan over time. Staying within the rated DoD (usually 85–90% for our batteries) is designed into normal daily use and isn't harmful.
Will my battery last as long in five years as it does today?
Capacity declines gradually over thousands of cycles, not suddenly. A quality LiFePO₄ battery used daily typically retains strong capacity for well over a decade before replacement becomes worth considering.
Can I check my real-time battery percentage and runtime estimate?
Yes — our monitoring dashboard shows live battery percentage, generation and consumption, so you're not guessing during an outage.