How Long Does a 100Ah Lithium Battery Last? Full Usage Breakdown
If you're prepping for outages, traveling, or going off-grid, knowing how long a 100Ah lithium battery lasts is essential. The answer depends on multiple factors, including the power load of your devices, battery chemistry, and inverter efficiency. In this guide, we break down everything you need to know from amp-hours and watt-hours to real-life usage scenarios so you can plan your energy use accurately and avoid getting caught without power when you need it most.
What Is a Lithium-Ion Battery?
Lithium-ion batteries are rechargeable batteries that use a carbon anode, lithium salt electrolytes, and variable cathodes, which may be made of lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), or others. They all work similarly; they create an electrical current using the movement of lithium ions, which we can then use to power our devices. When recharging, the ions flow in the opposite direction.
LiFePO4 batteries are the safest alternative to older lithium-ion models. They’re not prone to potentially dangerous thermal runaway, have a greater depth of discharge (100%), and offer more charging cycles (at least 3000), so they last much longer. This is why EVs and renewable energy systems are all starting to use this chemistry now.
Understanding Lithium-Ion Battery Capacity
Battery capacity tells us how much electric charge a battery can store, which helps determine how long it lasts. If you use the same appliances the same way, a 200Ah battery will last roughly twice as long as a 100Ah battery.
What Does Ampere-Hours (Ah) Mean?
We use ampere-hours (Ah, also called amp-hours) to measure capacity, where amps are the flow of electrical current and h is hours. To get Ah, multiply the amps by the number of hours. For instance, a 100Ah battery can deliver 100 amps for 1 hour or 1 amp for 100 hours.
Factors That Affect 100Ah Lithium-Ion Battery Runtime
The following factors are all critical considerations when estimating runtime.
Battery Capacity
Battery capacity tells us how much electric charge it can store, so it’s the primary factor in determining how long a battery can last. A larger capacity means a longer running time.
Connected Load
The next most important factor is the connected load. The higher the watts connected, the shorter the run time, since run time is inversely proportional to the number of connected watts. If you have a 100Ah battery with a 1000W load, but add another 1000W (2000W total), you halve your runtime. Conversely, cutting that load to 500W doubles your runtime.
Type of Battery
Even with the same amp-hour ratings, different batteries have different run times due to the depth of discharge (DoD). Lead-acid can only be discharged to about 50% of its capacity, older lithium-ion models have a DoD of 80%, and LiFePO4 has a DoD of about 100%. This means a LiFePO4 of the same Ah will last twice as long as a lead-acid model.
Battery Age and Condition
As batteries age, they lose some of their efficiency. Also, if batteries are discharged beyond their DoD, run under a heavier load, stored in extreme temperatures, or not appropriately maintained (mainly with lead-acid), their runtime will be reduced.
Discharge Rate
Discharge rate, often called the C-rate, is the maximum recommended discharge rate. By convention, a battery's capacity is 1C. If you have a 2C battery, you can discharge it at a current twice its capacity, halving its running time. Conversely, 0.5C means you can discharge at half the current, doubling the runtime. If you discharge a battery faster than its specified rate, the running time will be much shorter than expected.
Lead-acid batteries have poor discharge rates, often less than 0.2C, while LiFePO4 models may have discharge rates between 3C and 5C.
Self-Discharge Rate
Self-discharge is the charge a battery loses when in storage. Lead-acid self-discharges at about 4% per week. If you have a fully charged battery in storage for 4 months, you will only have 32% left (17 weeks x 4% = 68% self-discharged) and cannot use it without recharging first.
LiFePO4 has a very low self-discharge rate, roughly 2% per month. After 4 months, 92% of its capacity will be left, so you can still use it without charging your battery.
Temperature
Temperature can also affect runtime when it reaches extremes. High temperatures are less critical with lithium-ion models if you stay within the manufacturer’s recommendations. However, operating batteries at temperatures below 14°F often halves their run time. Fortunately, LiFePO4 batteries perform well in cold weather. Their operating temperatures are between -4°F and 140°F for discharge and 32°F and 113°F for charging.
How to Calculate 100Ah Lithium-Ion Battery Runtime
Use the following steps to calculate runtime under any usage scenario.
1. Calculate Capacity in Watt-Hours
First, convert your capacity from amp-hours(Ah) to watt-hours(Wh) because watt-hours better show how much energy is being consumed:
Wh=Ah x Voltage(V)
Most batteries work at 12V, so:
Wh = 100Ah x 12V = 1200Wh, which means it can provide 1200 watts for one hour.
2. Factor in Depth of Discharge
Now you need to consider the DoD, where:
Usable Capacity = Wh x DoD
For a lead-acid model (50% DoD): 1200Wh x 50%(0.5) = 600Wh
LiFePO4 has a DoD of 100%: 1200Wh x 100%(1.0) = 1200Wh
3. Inverter Efficiency
Most devices run on AC (alternating current), but batteries store energy as DC (direct current). We lose some energy when we use inverters to convert DC into AC. How much varies with the inverter, but let’s just say it's 90% efficient.
Our lead-acid battery has a net available capacity of: 600Wh x 90%(0.9) = 540Wh
And our LiFePO4 will have: 1200Wh x 90%(0.9) = 1080Wh
4. Calculate Run Time
Now we can calculate runtime using your total load or power consumption.
Say we have a 300W laptop and a 50W speaker.
Total Load = 300W + 50W = 350W
Now we can calculate runtime:
Run time = Net Capacity/Total Load
For our lead-acid battery: 540Wh/350W = 1.54 hours
For our LiFePO4 example: 1080Wh/350W = 3.09 hours
Common Usage Scenarios
Running Small Appliances
Running small appliances like LED lights, a fan, or a router gives you a much longer running time.
If you have a 20W router, using our above LiFePO4 example (1080Wh net capacity), your runtime is:
1080Wh/20W = 54 hours
That’s plenty of time to get you through an outage. You can even use a smaller battery if you only need it for a day. Fortunately, EcoFlow Solar Generators come in a wide range of capacities to suit any need.
Powering Medium Loads
Medium loads like TVs, laptops, and fridges have higher energy needs, reducing runtime. Let’s calculate the runtime for a 600W fridge:
1080Wh/600W = 1.8 hours
Supporting Heavy Equipment
Heavy equipment like power tools, inverters, microwaves, or dryers need more energy. Let’s say we have a 2000W circular saw:
1080Wh/2000W = 0.54 hours
This is why heavy equipment typically requires a large capacity. For instance, the EcoFlow DELTA Pro 3 has a 4096Wh capacity, which means it can run that same saw for at least 3 times longer than your 100Ah(1200Wh) battery.
Off-Grid and RV Use: Day-to-Day Expectations
For off-grid and RV use, add up your total load. If you have a 10W light, a 50W TV, and a 30W fan, your run-time would be:
1080Wh/(10W+50W+30W =90W) = 12 hours
The EcoFlow DELTA 3 Plus starts at 1024Wh capacity, which is perfect for most RV appliances.
Frequently Asked Questions
How Long Will a 100AH Lithium Battery Run a Fridge?
How long a 100Ah battery will run a fridge depends on its rated watts. A 500W fridge will run for about 2.4 hours. A lower-wattage fridge will run longer, and a higher-wattage one will have a shorter run time.
How Many Hours Will a 100AH Lithium Battery Last?
How long a 100Ah lithium battery will last depends entirely on the load connected to it. A 500W fridge can run slightly over 2 hours, while a 20W router can run for over 50 hours.
How Long Will a 100AH Battery Run a TV?
How long a TV will run on a 100Ah battery depends on its rated wattage. A 50W TV will last over 20 hours, while a 200W TV will last a bit more than 5 hours.
How Long Will a 100AH Lithium Battery Run a 1000W Inverter?
To calculate how long it will run a 1000W inverter, divide its capacity in Wh (100Ah = 1200Wh) by the inverter's wattage. So, run time = 1200Wh/1000W = 1.2 hours.
Final Thoughts
A single 100Ah lithium battery offers excellent versatility for small to medium energy needs, but actual runtime depends on your connected load, battery type, and conditions. Lithium iron phosphate (LiFePO4) batteries outperform older chemistries in depth of discharge, cycle life, and safety, offering better run times. Whether you're powering appliances, tools, or an RV, calculating your total wattage and considering inverter efficiency will help you choose the right solution. Fortunately, EcoFlow Solar Generators have various capacities for high-performance, scalable power to suit every need.