Calculating battery capacity for a home
To figure out how many batteries you need for your home, you need two numbers: average consumption in watts and desired autonomy time in hours. Multiply one by the other — that gives you required capacity in watt-hours. Add 20-25% reserve for inverter losses and incomplete discharge. Done.
Sounds simple, but in practice people err in both directions. Some buy a 5 kWh battery for a house with an electric boiler — and wonder why it lasts an hour. Others get 30 kWh for an apartment with a fridge and Wi-Fi — and overpay by three times. We will help you hit the target.
Step 1: determine your load
Make a list of appliances that will run during an outage. Not all of them — just those you actually need. Here are typical power values:
| Appliance | Power, W | Runs, hrs/day | Consumption, Wh/day |
|---|---|---|---|
| Refrigerator | 80-150 | 8-10 (compressor) | 800-1500 |
| LED lighting (5 fixtures) | 50-75 | 5-6 | 250-450 |
| Wi-Fi router | 10-15 | 24 | 240-360 |
| Phone chargers (2) | 20-40 | 3-4 | 60-160 |
| Laptop | 40-65 | 4-6 | 160-390 |
| TV | 60-120 | 3-4 | 180-480 |
| Well pump | 800-1500 | 1-2 | 800-3000 |
| Electric kettle | 1500-2200 | 0.1-0.2 | 150-440 |
| Air conditioner | 800-2000 | 4-8 | 3200-16000 |
Add up the "Consumption" column for your appliances. That is your daily consumption in watt-hours.
Example: apartment — minimal setup
Fridge + router + lights + chargers = roughly 1,500-2,500 Wh per day. That is 1.5-2.5 kWh. One 5 kWh module covers a full day with margin.
Example: house — comfortable setup
Everything from the apartment + TV + laptop + pump (1 hour per day) = 3,500-6,000 Wh. That is 3.5-6 kWh. One 5 kWh module is tight, two modules (10 kWh) give comfort.
Step 2: account for losses
The battery does not deliver 100% of stored energy. Three sources of loss:
- Inverter efficiency: 90-95%. So out of every 100 Wh from the battery, 90-95 Wh reaches the outlet
- Depth of discharge: LiFePO4 can discharge to 80-90%, but for longevity keep it above 20%. So realistically 80% of capacity is available
- BMS self-discharge: minimal (0.5-1% per month) but it exists
Combined factor: 0.93 (inverter) x 0.80 (depth of discharge) = 0.74. So from a 5.12 kWh module, roughly 3.8 kWh is actually available.
Step 3: the formula
Here is the simple formula we use for sizing:
Required capacity (kWh) = (Daily consumption x Days of autonomy) / 0.74
Examples:
- Apartment, 2 kWh/day, 1 day → 2 / 0.74 = 2.7 kWh → 5 kWh module
- Apartment, 2 kWh/day, 2 days → 4 / 0.74 = 5.4 kWh → 5 kWh (tight) or 10 kWh
- House, 5 kWh/day, 1 day → 5 / 0.74 = 6.8 kWh → 10 kWh
- House, 5 kWh/day, 2 days → 10 / 0.74 = 13.5 kWh → 15 kWh (3 modules of 5)
How many modules is that
A standard LiFePO4 module is 5.12 kWh (51.2 V, 100 Ah). Modules of 2.56, 7.68, 10.24, and 15.36 kWh exist, but 5.12 is the most popular size.
| Required capacity | 5 kWh modules | Or 10 kWh modules |
|---|---|---|
| Up to 3.8 kWh | 1 | — |
| 3.8 - 7.6 kWh | 2 | 1 |
| 7.6 - 11.4 kWh | 3 | 1 + extra 5 |
| 11.4 - 15.2 kWh | 3-4 | 2 |
| 15+ kWh | 4+ | 2+ |
What if you have solar panels?
Panels change the math. During the day the battery charges from the sun, so you only need to cover the nighttime period (8-12 hours) plus cloudy days.
A 3 kW solar panel array generates 12-18 kWh on a clear day. That is enough to fully charge a 10 kWh battery with energy to spare. On a cloudy day — 3-6 kWh.
Rule of thumb: with panels you can reduce battery capacity by 30-40% compared to grid-only backup.
Typical configurations from our clients
- 1-bedroom apartment: 3 kW inverter + 5.12 kWh battery. Budget — from 35,000 UAH. Autonomy — 10-16 hours
- 2-3 bedroom apartment: 5 kW inverter + 10.24 kWh battery. Budget — from 65,000 UAH. Autonomy — 8-14 hours
- House 80-120 m²: 5 kW inverter + 15 kWh battery + 3 kW panels. Budget — from 120,000 UAH. Autonomy — 1-2 days
- House 150+ m²: 8-10 kW inverter + 20-30 kWh battery + 5-8 kW panels. Budget — from 200,000 UAH
Frequently Asked Questions
How many batteries for a 100 m² house?
Depends on your appliances. Without electric heating — typically 10-15 kWh (2-3 modules of 5 kWh). With a heat pump — 20-30 kWh.
Is one 5 kWh module enough?
For an apartment with minimal load (fridge, router, lights, chargers) — yes, for 10-16 hours. For a house — probably not, unless you run only essentials.
How to measure consumption if I do not know appliance power?
Check the nameplate on the side or back of the appliance — power in watts is listed there. Or check the manual. A plug-in power meter (wattmeter) costs 200-300 UAH and shows real consumption.
Can I add modules later?
Yes. LiFePO4 modules connect in parallel. Start with one, add another in a month or a year. Key requirement — same brand and preferably same model.
Is 5 kWh a lot or a little?
5 kWh is roughly 14 hours of fridge + router + lighting. Enough for an apartment. For a house with a pump — minimum, 10 kWh is better.
Summary
Calculate daily consumption, divide by 0.74, round up to the nearest module. For an apartment — one 5 kWh module, for a house — two or more. Browse the LiFePO4 battery catalog with current prices on our website.
