Batteries for solar systems are almost always labeled in ampere-hours (Ah), but the energy they store is measured in kilowatt-hours (kWh). To compare batteries, calculate system runtime, or size a solar array, you must convert Ah to kWh.

The conversion is simple, but the catch is that voltage matters. A "200 Ah battery" at 12V stores very different energy than a "200 Ah battery" at 48V. This guide explains the math, provides lookup tables, and reveals why manufacturers use Ah instead of kWh on labels.

                    Quick Answer: kWh = Ah × V ÷ 1000. A "200 Ah" battery at 12V = 2.4 kWh. The same "200 Ah" battery at 48V = 9.6 kWh. Always check voltage before comparing Ah numbers.
                

The Core Formula

Energy (kWh) = Ah × Voltage (V) ÷ 1000

To convert the other direction:

Ah = (kWh × 1000) ÷ Voltage (V)

Example: A 48V lithium battery rated at 100 Ah:

Energy = 100 × 48 ÷ 1000 = 4.8 kWh

Ah to kWh Conversion Table (12V, 24V, 48V)

Use this table to quickly convert common battery Ah ratings to kWh at the three standard solar battery voltages.

Ah Rating	kWh at 12V	kWh at 24V	kWh at 48V	Common Application
50 Ah	0.60 kWh	1.20 kWh	2.40 kWh	Small UPS, single appliance backup
100 Ah	1.20 kWh	2.40 kWh	4.80 kWh	Small solar backup, RV
150 Ah	1.80 kWh	3.60 kWh	7.20 kWh	Medium home, essential loads
200 Ah	2.40 kWh	4.80 kWh	9.60 kWh	Standard home backup with tubular
250 Ah	3.00 kWh	6.00 kWh	12.00 kWh	Larger home, full essential loads
300 Ah	3.60 kWh	7.20 kWh	14.40 kWh	Large home with AC intermittent
400 Ah	4.80 kWh	9.60 kWh	19.20 kWh	Full home backup
500 Ah	6.00 kWh	12.00 kWh	24.00 kWh	Large off-grid home
1,000 Ah	12.00 kWh	24.00 kWh	48.00 kWh	Commercial or large estate

                    Critical Observation: A "200 Ah battery" can be anything from 2.4 kWh (12V) to 9.6 kWh (48V). When a seller advertises a "200 Ah battery," always ask: at what voltage? The same Ah number means 4x more energy at 48V than at 12V.
                

Reverse Conversion: kWh to Ah

If you know your required energy in kWh and need to find the battery Ah rating:

Ah = (kWh × 1000) ÷ Voltage

Example: You need 10 kWh of storage. What Ah at different voltages?

Required Energy	Ah at 12V	Ah at 24V	Ah at 48V
5 kWh	417 Ah	208 Ah	104 Ah
10 kWh	833 Ah	417 Ah	208 Ah
15 kWh	1,250 Ah	625 Ah	313 Ah
20 kWh	1,667 Ah	833 Ah	417 Ah

Why Do Manufacturers Label Batteries in Ah Instead of kWh?

There are two reasons battery labels show Ah rather than kWh:

1. Ah is a larger number for the same energy. A 48V 100 Ah battery stores 4.8 kWh. Marketers prefer "100 Ah" over "4.8 kWh" because 100 is a bigger number. A 300 Ah battery at 48V sounds huge, but it's only 14.4 kWh.

2. Ah is application-agnostic. The same battery can be used in a 12V, 24V, or 48V system. The manufacturer doesn't know which voltage you will use, so they label the battery with its fundamental charge capacity (Ah) and let you calculate energy based on your system voltage.

Tip: When comparing two batteries, always convert both to kWh at the same voltage. A "150 Ah, 12V" battery (1.8 kWh) is NOT comparable to a "100 Ah, 48V" battery (4.8 kWh), even though the Ah numbers are close. The 48V battery stores 2.7x more energy.

The C-Rate Trap: Ah Rating Is Not Fixed

A battery's Ah rating depends on the discharge rate, measured in C-rate. A battery rated at C/20 means the capacity is measured over a 20-hour discharge. If you discharge faster, the effective capacity drops.

Important: A "200 Ah" tubular battery (C/10 rating) delivers 200 Ah only if discharged over 10 hours at 20 A. If you discharge at 50 A (a 4-hour rate), the effective capacity may drop to 170 Ah or less — that's a 15% reduction in usable energy. Always check the C-rate on the label.

Battery Chemistry	Standard C-Rate	Capacity @ 2x Rate	Capacity @ 5x Rate
Tubular Lead-Acid	C/10 (10 hr discharge)	92-95%	75-85%
AGM Lead-Acid	C/20 (20 hr discharge)	90-93%	70-80%
Lithium LiFePO4	C/5 (5 hr discharge)	98-100%	95-98%
Lithium NMC	C/3 (3 hr discharge)	98-100%	95-97%

Example: A tubular battery rated 200 Ah at C/10 (20 A discharge over 10 hours) might deliver only 160 Ah when powering an air conditioner that draws 50 A over 4 hours. This means your actual usable kWh is 20% less than the label suggests.

                    Practical Rule: For lead-acid batteries, multiply the label Ah by 0.85 for a realistic real-world estimate at typical home loads. For lithium, multiply by 0.97. This C-rate derating is why many solar installers oversize lead-acid banks by 15-20%.
                

Worked Example: Reading a Battery Label

Scenario: You find a battery labeled "Luminous ILST 15027 - 150 Ah at C/10, 12V."

Step 1: Voltage = 12V. Ah rating = 150 Ah at C/10 (15 A discharge for 10 hours).

Step 2: Label energy = 150 × 12 ÷ 1000 = 1.8 kWh.

Step 3: Real-world energy for a 3-hour backup load (50 A discharge): roughly 130 Ah × 12 ÷ 1000 = 1.56 kWh (13% loss).

Step 4: With 50% DoD for lead-acid: Usable = 1.56 × 0.50 = 0.78 kWh.

That "150 Ah" battery provides less than 0.8 kWh of usable energy in a real solar backup scenario. Understanding Ah-to-kWh and DoD and C-rate is essential to avoid undersizing a battery bank.

Related Guides

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How Solar Metrix Pro Helps: The Battery Backup Sizing Calculator in the sidebar above handles the math. Enter your day and night loads, backup hours, and system voltage. It instantly compares tubular lead-acid vs lithium capacities, energy waste, and recommends the best chemistry for your needs.
                

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Data sources: Battery manufacturer datasheets (Luminous, Exide, Trojan, Amaron; BYD, Pylontech, CATL). C-rate derating curves from industry standard IEC 61427 testing. Pricing and specifications indicative Q2 2026. Always verify actual C-rate performance with the specific battery model's datasheet.

Last updated: July 2026 | Browse all guides

Battery Ah to kWh Conversion: Read Your Spec Label