How do you convert amp-hours to watt-hours?

Multiply amp-hours by voltage. The formula is Wh = Ah x V. For example, a 100Ah battery at 12V contains 1,200 Wh (100 x 12). At 24V, the same 100Ah rating gives 2,400 Wh. The voltage of the battery is the key factor that determines total energy.

How many watt-hours is a 100Ah 12V battery?

A 100Ah 12V battery stores 1,200 Wh (1.2 kWh) of total energy. However, the usable energy depends on chemistry: a lithium LiFePO4 battery provides roughly 960-1,080 Wh usable (80-90% depth of discharge), while a lead-acid battery provides about 600 Wh usable (50% depth of discharge).

What is the difference between amp-hours and watt-hours?

Amp-hours (Ah) measure charge capacity -- how much current a battery can deliver over time. Watt-hours (Wh) measure energy capacity -- how much total work a battery can do. Watt-hours account for voltage, which is why Wh is the better metric for comparing batteries at different voltages. A 100Ah 12V battery and a 50Ah 24V battery both store exactly 1,200 Wh.

Why do battery manufacturers use amp-hours instead of watt-hours?

Amp-hours has been the traditional rating for lead-acid batteries because voltage was assumed (12V for automotive, 6V for golf carts). Modern home battery systems like the Tesla Powerwall list capacity in kWh because they operate at higher voltages (48V+) where the Ah number alone is not meaningful to consumers. The industry is slowly shifting toward kWh ratings.

Does a 200Ah battery last twice as long as a 100Ah battery?

At the same voltage and load, yes -- approximately twice as long. A 200Ah 12V battery stores 2,400 Wh compared to 1,200 Wh for a 100Ah 12V battery. However, very high discharge rates reduce effective capacity in lead-acid batteries due to the Peukert effect. Lithium batteries are largely unaffected by discharge rate.

How do I convert Ah to kWh?

First convert Ah to Wh using Wh = Ah x V, then divide by 1,000 to get kWh. For example, a 200Ah 12V battery: 200 x 12 = 2,400 Wh, divided by 1,000 = 2.4 kWh. For a 200Ah 48V battery: 200 x 48 = 9,600 Wh = 9.6 kWh.

What is the usable watt-hours of a battery after depth of discharge?

Multiply the total Wh by the recommended depth of discharge (DoD). Lithium LiFePO4 batteries allow 80-100% DoD, so a 1,200 Wh lithium battery provides 960-1,200 Wh usable. Lead-acid batteries should not exceed 50% DoD, so a 1,200 Wh lead-acid battery provides only 600 Wh usable. Always size your battery bank based on usable capacity, not total.

Amp-Hours To Watt-Hours Calculator (Ah To Wh Conversion)

Watt-hours = Amp-hours x Volts. That is the entire formula. A 100Ah battery at 12V stores 1,200 Wh. The same 100Ah rating at 48V stores 4,800 Wh -- four times the energy. This guide explains the conversion, provides a reference table for common battery sizes, and covers the real-world factors (depth of discharge, efficiency losses, temperature) that reduce usable energy below the theoretical number.

Calculator

Battery voltage

Battery capacity

Battery chemistry

Target charge time

hrs

Required solar panel size

To charge a 100Ah 12V Lithium (LiFePO4) battery in 5 hours

Energy to charge

1.26kWh

If you use 100W panels

panels needed

If you use 200W panels

panels needed

171 kg

CO₂ avoided per year

0.04

equivalent US homes powered

trees planted equivalent

$74

estimated annual savings

Chemistry	Efficiency	Cycle Life	Panel Watts
Lithium (LiFePO4)	95%	3,000–5,000	252 W
Deep Cycle AGM	85%	500–1,000	283 W
Lead-Acid Flooded	80%	300–500	300 W

Tap to see sensitivity analysisSensitivity analysis

Sensitivity range
Scenario	Value
Low (-20%)	202 W
Expected	252 W
High (+20%)	302 W

Battery chemistry has the biggest effect \u2014 switching from lead-acid to lithium reduces required panel watts by ~20%.

What size battery do I need?See production for your state

The Formula: Wh = Ah x V

The conversion from amp-hours to watt-hours requires one piece of information beyond the Ah rating: the battery's nominal voltage.

Wh = Ah x V

Where:

Wh = watt-hours (total energy stored)
Ah = amp-hours (charge capacity)
V = nominal voltage of the battery

This formula comes directly from the relationship between power and current. Power (watts) equals voltage times current (W = V x A). Extend that over time, and energy (watt-hours) equals voltage times charge (Wh = V x Ah).

Why This Conversion Matters

Amp-hours tell you how much charge a battery can deliver. Watt-hours tell you how much energy it stores. The difference is critical for solar battery sizing because your appliances consume energy in watts, not amps.

If you know your daily energy usage is 5,000 Wh and you are choosing between a 12V and 48V battery bank, you need very different Ah ratings to store the same energy:

12V system: 5,000 / 12 = 417 Ah needed
48V system: 5,000 / 48 = 104 Ah needed

Both store 5,000 Wh. The 48V system just does it with fewer amp-hours (and thinner wires, which is one reason 48V is preferred for larger systems).

Common Battery Sizes: Ah To Wh Conversion Table

Battery	Voltage	Ah Rating	Watt-Hours (Wh)	Kilowatt-Hours (kWh)
Small sealed lead-acid	12V	7 Ah	84 Wh	0.08 kWh
Marine/RV deep cycle	12V	100 Ah	1,200 Wh	1.2 kWh
Large deep cycle	12V	200 Ah	2,400 Wh	2.4 kWh
Golf cart battery	6V	225 Ah	1,350 Wh	1.35 kWh
LiFePO4 (common)	12V	100 Ah	1,200 Wh	1.2 kWh
LiFePO4 server rack	48V	100 Ah	4,800 Wh	4.8 kWh
LiFePO4 server rack	48V	200 Ah	9,600 Wh	9.6 kWh
Tesla Powerwall 3	48V	~281 Ah	13,500 Wh	13.5 kWh
EG4 LL-V2	48V	100 Ah	5,120 Wh	5.12 kWh

Note: the Tesla Powerwall 3 operates at a nominal 48V and stores 13.5 kWh, which works out to approximately 281 Ah.

How Voltage Changes Everything

The same Ah rating means very different amounts of stored energy depending on voltage. Here is 100Ah at each common battery voltage:

Voltage	100 Ah Equals	Typical Use Case
6V	600 Wh (0.6 kWh)	Golf cart batteries, wired in series for 12V/24V/48V
12V	1,200 Wh (1.2 kWh)	RVs, boats, small off-grid cabins
24V	2,400 Wh (2.4 kWh)	Mid-size off-grid, some inverters
36V	3,600 Wh (3.6 kWh)	E-bikes, some marine systems
48V	4,800 Wh (4.8 kWh)	Whole-home battery backup, large off-grid

This is why comparing batteries by amp-hours alone is misleading. A 100Ah 48V battery stores four times the energy of a 100Ah 12V battery. Always convert to watt-hours (or kilowatt-hours) before comparing.

Real-World vs Theoretical Capacity

The Wh = Ah x V formula gives you the total energy stored in the battery. The amount you can actually use is always less due to three factors.

Depth of Discharge (DoD)

No battery should be drained to zero. The recommended maximum depth of discharge depends on chemistry:

Chemistry	Max DoD	Usable Energy from 1,200 Wh Battery
Lithium LiFePO4	80-100%	960-1,200 Wh
AGM (sealed lead-acid)	50%	600 Wh
Flooded lead-acid	50%	600 Wh
Gel	50%	600 Wh

A 100Ah 12V lead-acid battery stores 1,200 Wh on paper but only delivers 600 Wh before you should recharge it. Draining beyond 50% dramatically shortens lead-acid cycle life. Lithium LiFePO4 batteries tolerate deep discharge much better -- most manufacturers warrant them to 80% DoD for 4,000-6,000 cycles.

Inverter Efficiency

If you are converting the battery's DC power to AC (which most home setups do), the inverter consumes 5-15% of the energy in the conversion. A typical inverter runs at 90-95% efficiency. Factor this in:

Usable AC Wh = Total Wh x DoD x Inverter Efficiency

For a 100Ah 12V lithium battery powering AC loads through a 93% efficient inverter at 90% DoD:

1,200 Wh x 0.90 x 0.93 = 1,004 Wh usable AC energy

Temperature Effects

Battery capacity drops in cold weather. A lead-acid battery at 0 degrees Celsius delivers roughly 80% of its rated capacity. At -20 degrees Celsius, it drops to about 50%. Lithium LiFePO4 batteries handle cold better but still lose 10-20% capacity at freezing temperatures and should not be charged below 0 degrees Celsius without a heated BMS.

For outdoor or unheated installations, add a 10-20% capacity buffer to your calculations.

Worked Example: Sizing a Battery Bank

You want to run a 1,500 Wh daily load (lights, phone chargers, router, laptop) from a battery bank with one day of autonomy.

Step 1 -- Total energy needed: 1,500 Wh

Step 2 -- Account for DoD. Using lithium at 90% DoD: 1,500 / 0.90 = 1,667 Wh total battery capacity needed.

Step 3 -- Account for inverter loss. At 93% efficiency: 1,667 / 0.93 = 1,792 Wh.

Step 4 -- Convert to Ah. At 12V: 1,792 / 12 = 149 Ah. At 48V: 1,792 / 48 = 37 Ah.

You would need a 150Ah 12V lithium battery (or two 100Ah in parallel for headroom), or a single 50Ah 48V lithium battery.

With lead-acid at 50% DoD: 1,500 / 0.50 / 0.93 = 3,226 Wh, which is 269 Ah at 12V -- more than double the lithium requirement.

When To Use Wh vs Ah

Use Wh (or kWh) when comparing batteries at different voltages, sizing a system to meet daily energy needs, or calculating how long a battery will run a specific load.
Use Ah when selecting charge controllers, sizing fuses and wire gauge (these depend on current, not energy), or when all your batteries are at the same voltage.

In practice, convert to Wh for planning and back to Ah for component selection.