Key takeaways
- Size by energy (kWh) for how long you need power, and by power (kW) for how much runs at the same time.
- Plan on about 81% of a battery’s rated kWh reaching your outlets: 90% usable depth of discharge × roughly 90% inverter efficiency.
- Essentials for a 12-hour outage usually fit one 5.12kWh battery. Shifting 10kWh of solar to the evening needs about 15kWh of batteries.
- Induxora 48V batteries connect up to 15 in parallel, so you can start small and add units of the same model later.
“How many batteries do I need?” has two answers: one for how long you want power, and one for how much you want to run at once. Get both right and the battery bank will carry your home through an outage or an evening without tripping your inverter. This guide walks through the five steps we use when sizing a system for a customer, with three worked examples.
Step 1: Decide what you want to back up
Start with the goal, because it changes the answer by a factor of five or more:
- Essentials backup: fridge, lights, Wi-Fi, phone charging, maybe a TV. The smallest and cheapest system.
- Solar self-consumption: store daytime solar and use it in the evening, every day.
- Whole-home or off-grid: everything, including large loads like well pumps or air conditioning, for one or more days without the grid.
Step 2: Add up your daily energy in kWh
For each appliance, multiply its running power by the hours you will use it, then add everything up:
Energy (kWh) = power (W) × hours ÷ 1,000
Example: a fridge averaging 150W over 12 hours uses 150 × 12 ÷ 1,000 = 1.8kWh.
Use the wattage on each appliance’s label, or better, measure it with a plug-in energy meter. Fridges and freezers cycle on and off, so their average power is much lower than the label. If you have solar or a smart meter, your monitoring app already shows your real evening and daily usage, which is the most accurate number you can use.
Step 3: Convert rated kWh to usable kWh
Not every kilowatt-hour on the label reaches your outlets. Two factors reduce it:
- Depth of discharge (DoD): Induxora home batteries are designed for 90% depth of discharge, which protects cycle life.
- Inverter efficiency: converting DC battery power to AC loses energy. We assume about 90% here. Check your inverter’s datasheet for its actual figure.
Together that is 0.90 × 0.90 ≈ 0.81, so plan on about 81% of rated capacity:
| Battery (51.2V) | Rated energy | Planning figure (≈81%) |
|---|---|---|
| 100Ah | 5.12kWh | 4.15kWh |
| 200Ah | 10.24kWh | 8.29kWh |
| 300Ah | 15.36kWh | 12.44kWh |
| 314Ah | 16.08kWh | 13.02kWh |
Step 4: Check power, not just energy
Energy tells you how long the batteries last. Power tells you how much can run at the same moment. A battery’s continuous discharge current sets its power limit: at 51.2V, a 100A battery delivers about 5.1kW and a 200A battery about 10.2kW.
Add up the loads that might run together (for example an electric kettle, microwave and fridge at dinner time) and make sure both your inverter and your battery bank can supply that. Motors such as well pumps and air conditioners draw a short surge when they start, so check your inverter’s surge rating too. If one battery’s current limit is too low for your peak loads, a second battery in parallel or a model with a higher discharge rating solves it. Your installer should confirm the bank’s combined limits against the user manual.
Step 5: Add a margin and plan for growth
Add about 20% on top of your calculated need. Usage varies day to day, batteries lose a little capacity over the years, and cold rooms reduce available energy. If your budget is tight, start with what covers your essentials. Induxora 48V batteries support up to 15 units in parallel, so you can add batteries of the same model later.
Worked examples
Example A: essentials through a 12-hour outage
| Load | Average power | Hours | Energy |
|---|---|---|---|
| Fridge | 150W | 12 | 1.80kWh |
| LED lights | 200W | 6 | 1.20kWh |
| Router and modem | 20W | 12 | 0.24kWh |
| TV | 100W | 4 | 0.40kWh |
| Phones and laptops | – | – | 0.10kWh |
| Total | 3.74kWh |
With a 20% margin that is about 4.5kWh. One 5.12kWh battery (4.15kWh planning figure) covers most of it, and two cover it comfortably or stretch it to a full day.
Example B: using 10kWh of solar every evening
Your solar app shows you use about 10kWh between sunset and sunrise. You need 10 ÷ 0.81 ≈ 12.4kWh of rated capacity. One 15.36kWh battery, or three 5.12kWh batteries, does the job with some margin.
Example C: an off-grid cabin with two days of autonomy
The cabin uses 8kWh a day, and you want two cloudy days of reserve: 16kWh. You need 16 ÷ 0.81 ≈ 19.8kWh of rated capacity. Two 10.24kWh batteries (20.48kWh) fit. Add the 20% margin and a third battery becomes worth considering.
Frequently asked questions
Is it better to buy one large battery or several small ones?
One large battery keeps wiring simple and usually costs less per kWh. Several smaller units let you spread the cost over time and give you more combined discharge current. Both work, as long as all batteries in a parallel bank are the same model.
Can I add batteries later?
Yes. Our 48V batteries support up to 15 units of the same model in parallel. Follow the parallel connection steps in the user manual, or ask us before you expand.
Where should the batteries be installed?
Indoors. Induxora home batteries are rated IP20, so install them in a garage, utility room or similar indoor space. They charge between 0 and 55°C (32 to 131°F).
Next steps
Write down your loads and hours, run the numbers above, and pick a form factor (wall-mount, stackable or server rack). If you would rather have us do it, send us your appliance list or inverter model and we will size the system for you.
