Solar Battery Calculator

Size the right battery for your solar system. Enter the load you want backed up and for how long, and get the battery size in kWh and Ah, and how many batteries that means, for both lithium and lead-acid.

Battery kWh = backup load (W) × hours ÷ 1,000 ÷ 0.85 ÷ depth of discharge. Example: 800 W of essentials for 4 hours needs about 4.4 kWh of lithium or 7.5 kWh of lead-acid (about 185 Ah or 315 Ah at 24 V). On-grid systems need no battery; add one only for backup.

Size Your Backup Battery

Backup load (watts) Add up what must run during a power cut. Example: 3 fans + 6 lights + fridge + TV + Wi-Fi ≈ 800W. Build it precisely with the solar load calculator.

Backup duration (hours)

Battery bank voltage

Your Battery Recommendation

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lithium battery (85% usable)

Energy to store–

Lithium capacity in Ah–

Lead-acid equivalent–

Lead-acid in Ah–

Indicative cost (lithium)–

Indicative cost (lead-acid)–

Backup estimate: real runtime depends on the battery brand, inverter and temperature. Ask a local solar contractor to confirm the battery size and current price for your loads.

Built and maintained by Solar Calculators Pro · Depth of discharge and inverter losses we apply

Battery Size for Common Backup Scenarios

Backup Scenario	Load	4-hr Lithium	4-hr Lead-Acid
Essentials (fans, lights, Wi-Fi)	~400 W	2.2 kWh	3.8 kWh
Essentials + fridge + TV	~800 W	4.4 kWh	7.5 kWh
Above + 1 ton AC	~1,700 W	9.4 kWh	16 kWh
Whole home with 1.5 ton AC	~2,500 W	13.8 kWh	23.5 kWh

Running ACs on battery is expensive: every hour of a 1.5 ton AC consumes as much stored energy as an entire evening of essentials. Most homes back up essentials only and leave heavy loads on grid or daytime solar.

Battery Ah to kWh: How Much Energy Is Usable

Batteries are sold in Ah, but backup depends on usable kWh = volts × Ah ÷ 1,000 × depth of discharge (50% for lead-acid, 85% for lithium):

Battery	Stored energy	Usable (lead-acid)	Usable (lithium)
12 V 100 Ah	1.2 kWh	0.6 kWh	1.0 kWh
12 V 150 Ah	1.8 kWh	0.9 kWh	1.5 kWh
12 V 200 Ah	2.4 kWh	1.2 kWh	2.0 kWh
24 V 150 Ah (2 × 12 V)	3.6 kWh	1.8 kWh	3.1 kWh
48 V 100 Ah	4.8 kWh	2.4 kWh	4.1 kWh
48 V 200 Ah	9.6 kWh	4.8 kWh	8.2 kWh

The inverter loses about 15% more on the way to your appliances, which the calculator above includes.

Lithium vs Lead-Acid for Solar Storage

Usable capacity: lithium (LiFePO4) delivers about 85% of its rating; lead-acid only about 50% before lifespan suffers. That is why the lead-acid bank above is nearly double the size.
Cycle life: lithium lasts 3,000 to 6,000 cycles (10+ years of daily use); lead-acid typically 800 to 1,500 cycles (3 to 5 years).
Cost: lithium costs about ₹18,000/kWh installed versus ₹9,000/kWh for lead-acid, but per usable kWh over its life, lithium is now cheaper for daily-cycling solar use.
Charging: lithium accepts fast charging from solar; lead-acid needs a slower, staged charge. Check how long your panels take to refill the bank with the battery charging time calculator.

Decide What Actually Needs Backup Before You Size

Battery budgets are made or destroyed by one decision: the backup list. Walk the house during an imagined evening power cut and sort loads into three buckets:

Must run: fans, lights, Wi-Fi, phone charging, the fridge. Typically 600 to 900W. This list alone keeps battery costs sane.
Nice to run: TV, a computer, the water pump for one fill. Add 300 to 900W and size the hours honestly; a pump runs minutes, not hours.
Luxuries that break budgets: ACs and geysers. Each AC hour drains 1.2 to 1.5 kWh; backing one up for 4 hours nearly triples the bank. Most homes leave heat and cooling off the backup bus.

Then pick hours from your outage reality: urban feeders with 1 to 2 hour cuts need 3 to 4 hours of autonomy; rural evening-outage areas need 6+. Build the wattage list precisely in the solar load calculator first if you have not.

Six Hours of Backup in Gurugram

A Gurugram home wants fans, lights, fridge, TV, Wi-Fi and one computer (about 1,100W) protected for 6-hour evening cuts. Energy needed: 6.6 kWh. After inverter losses and safe depth of discharge, that is 9.1 kWh of lithium (about 190 Ah at 48V) or a hefty 15.5 kWh of lead-acid. Indicative cost: roughly ₹1.65 lakh lithium versus ₹1.4 lakh lead-acid, and the lithium bank will outlive two lead-acid replacements, which is the real comparison. Halving the backup window to 3 hours halves every number above: hours are the cheapest thing to negotiate with yourself.

After Sizing: Buying the Battery Right

Read warranties in cycles, not years. "5 years or 3,000 cycles at 80% DoD" tells you the real service life; a year figure alone hides the cycling assumption.
Match bank voltage to the inverter. 24V suits small backup; 48V is the modern default above 2 kWh because it halves currents and cable sizes (see the wire size calculator).
LiFePO4 is the lithium to buy. For homes, its thermal stability and 3,000 to 6,000 cycle life make it the standard; other lithium chemistries belong in vehicles.
Plan the recharge. A bank your panels cannot refill by evening protects you exactly once; check the loop with the charging time calculator.

Battery Buying Errors

Backing up the whole house "to be safe". Whole-home backup triples cost for loads nobody misses during a two-hour cut; the must-run list is the honest baseline.
Sizing lead-acid like lithium. Lead-acid delivers only half its label safely; a 150Ah tubular is not 150Ah of usable anything.
Ignoring inverter losses. The 15% conversion loss compounds daily; this calculator includes it, but hand-sized banks usually do not.
Oversizing hours for a rare storm. Designing for the once-a-year 12-hour outage doubles the bank you cycle daily; a small generator or graceful load-shedding covers the black swan cheaper.

How Backup kWh Is Calculated

Energy needed = Backup load (W) × Hours ÷ 1000
Battery kWh = Energy ÷ 0.85 inverter efficiency ÷ DoD (0.85 lithium / 0.50 lead-acid)
Capacity (Ah) = Battery kWh × 1000 ÷ Bank voltage

Battery settings

Inverter efficiency: 85% from battery terminals to appliances
Depth of discharge: 85% lithium (LiFePO4), 50% lead-acid (tubular)
Costs: ~₹18,000/kWh lithium, ~₹9,000/kWh lead-acid, installed, 2026 indicative

Pair the battery with the right electronics using the solar inverter size calculator.

Solar Battery FAQs

What size battery do I need for a power cut of 4 hours?+

For an essentials load of about 800W (fans, lights, fridge, TV, Wi-Fi), you need roughly 4.4 kWh of lithium or 7.5 kWh of lead-acid. At 24V, that is about 185 Ah lithium or 315 Ah lead-acid.

How many batteries are needed for a 3kW solar system?+

The battery is sized to your backup load and hours, not the panel kW. A typical 3 kW hybrid home pairs 4 to 6 kWh of lithium storage, which covers essentials for 4 to 6 hours. Longer or heavier backup scales the bank up proportionally.

Which battery is best for solar: lithium or lead-acid?+

For daily-cycling solar use, lithium (LiFePO4) wins on lifespan, usable capacity, footprint and maintenance, and its per-cycle cost is now lower. Lead-acid still makes sense for rarely-used backup where upfront cost dominates.

What does 150Ah battery mean in kWh?+

Multiply Ah by voltage: a 12V 150Ah battery stores 1.8 kWh gross. Usable energy is less: about 0.9 kWh at 50% DoD for lead-acid. Two such batteries in series make a 24V 150Ah bank, still 3.6 kWh gross.

Can a solar battery run an air conditioner?+

Yes, with a big enough bank and inverter, but expect roughly 1.2 to 1.5 kWh consumed per hour for a 1.5 ton inverter AC. Backing up one AC for 4 hours needs about 9 kWh of lithium, which is why most homes exclude ACs from backup.

Do on-grid solar systems need a battery?+

No. On-grid systems work without storage and shut down during outages for safety. Add a battery only if you face real power cuts; then a hybrid inverter with a right-sized bank, as calculated here, is the way to go.

How long will a 5kWh battery run my house?+

On an essentials load of 800W, about 5 hours of lithium capacity (85% usable through a 85%-efficient inverter yields ~3.6 kWh delivered). Add an AC and the same battery empties in under 2 hours, which is why the backup list matters more than the battery brand.

Is it worth adding a battery to an existing on-grid system?+

Only if power cuts genuinely disrupt you. You will need a hybrid inverter swap plus the bank, typically ₹60,000 to ₹1.5 lakh, and it adds zero bill savings. Stable-grid homes get better returns from more panels instead.

How many batteries are required for a 5kW solar system?+

It depends on your backup load and hours, not on the 5 kW of panels. Backing up 1,000 W for 5 hours needs about 7 kWh of lithium, for example a 48 V 150 Ah bank, or about 12 kWh of lead-acid, for example four 12 V 250 Ah batteries in series.