How long will 100ah battery last on a load? Let's find out!
Most search results for 100Ah battery runtime will provide a “theoretical” estimate. Yet, real-world results may differ.
how long will 100ah battery last calculator
- The result takes into account the efficiency of an inverter (90%) and the efficiency of the battery discharge (lead acid: 85%, Lithium: 95%).
Battery state of charge (SoC) refers to the amount of charge it has relative to its total capacity. A fully charged battery has an SoC of 100%.
Example: How Long Will A 100ah Battery Run An Appliance That Requires 400 Watts?
- Battery capacity: 100ah
- Battery voltage: 12v
- Battery type: Lithium
- Battery state of charge: 100% charged
- Battery depth of discharge limit: 100%
- Load connected through the inverter? Yes
- Total load: 400 watt
5 Steps To Calculate 100ah Battery Runtime
1. Calculate the battery capacity in watts
Watt is a measurement unit for total energy (watt = amps × volts). Using watts to measure the battery capacity will make it easier --- because most home devices have their power listed in watts.
Also, you can find out how much ACTUAL energy your battery can store using this method.
For example: A 24V 100Ah battery has the capacity to store twice as much power as a 12V 100Ah battery.
Formula: Battery watt-hours = Battery (Ah) × Battery Volts
100ah battery in watt-hours = 100 × 12 = 1200 watt-hours
2. Consider the battery Depth of Discharge
Depth of Discharge measures the amount of energy taken from the battery and how much remains. A high DoD shows that you have used more energy from the battery, while a low DoD means you have used less.
Default battery depth of discharge limit:
- Lead-acid battery: 50% DoD limit
- Lithium: 100% DoD limit
Let's say you have a lead acid battery.
Battery capacity in wh after DoD limit = 1200 × 50% = 600wh
3. Consider the discharge efficiency rate
Multiplying the battery capacity after DoD by 0.85 for lead acid and 0.95 for lithium-ion.
Unfortunately, batteries are not 100% efficient when discharging. The efficiency rate will depend on many factors, including — how heavy the load is, battery chemistry (lead acid vs lithium), battery temperature, and self-discharge rate.
Based on directscience.com data:
- Lead-acid batteries discharge efficiency ≈ 80 − 85%
- Lithium-ion batteries discharge efficiency ≈ 90 − 95%
I'll carry on with a lead acid type battery.
Battery capacity after discharge efficiency = 600 × 0.85 = 510wh
4. Consider the inverter efficiency
Multiply the battery capacity after the DoD limit with the inverter efficiency rate.
Batteries store power in DC (direct current) but most of our household appliances need AC (alternating current). So to run appliances, you need an inverter that will convert the DC into AC.
Unfortunately, inverters are not 100% efficient. Most of them are about 90% efficient.
Battery AC watts = 510 × 90% = 460 AC watt-hours
5. Final step (calculation)
100ah battery runtime on 100w appliance = 540 ÷ 100 = 4.6 hours
Now let's discuss some shortcomings and drawbacks of these methods.
The Problems and Shortcomings of These Strategies
1. Battery Life
Every time you charge and discharge a battery to its Depth of Discharge (DoD) limit, its storage capacity decreases, known as a cycle.
If you have used your battery for a few hundred cycles, then the result will be different. This factor isn't included in my above-given methods.
Lead acid batteries lose 20% of their charge-holding capacity after 500 cycles. And lithium batteries at 2000 cycles (ask your manufacturer to get the most accurate number).
2. battery discharge mechanism
Especially, lead-acid batteries are designed to be discharged in 20 hours to maintain battery health and optimize efficiency. For example, it's recommended to discharge a 100Ah lead-acid battery at 5 amps.
But, AGM and lithium (LiFePO4) batteries can handle a higher discharge rate (usually, 50% of their capacity). Ask your manufacturer to get the most accurate number.
If you take the power out of your battery too fast, it will get hot inside and lose some of its power. This factor isn't included in the above methods.
For example, if you discharge your lead-acid battery with 100 amps, Theoretically it should last 30 minutes (keep in mind the 50% DoD limit) but may last about 10 → 15 minutes.
Check the battery discharge rate on its specs sheet or it'll be mentioned on the battery (1h → 1C, 2h → 0.5C, 5h → 0.2C, etc).
3. external battery temperature
Batteries perform their best at room temperature. The temperature at which batteries operate the best is 68ºF or 20ºC (Ask your manufacturer to get the most accurate number).
A higher or lower temperature (than what's recommended) will affect the battery's performance. A rule of thumb is "an increase of temperature to 77ºF or 25º C can reduce battery performance by 50%".
tips to increase battery efficiency
Here are some tips to increase the performance/efficiency of your batteries.
- Choose the right size wire from the battery to the inverter. The size of the wire will depend on the load. The higher the load is, the thicker wire you need.
- Store your battery in the recommended temperature range. Usually, it is between –20°C to 50°C for lead acid and –20°C to 60°C for lithium-ion.
- Do not discharge your battery at a higher rate. The max discharge rate should be — Lead-acid; 25% of its total capacity, Lithium battery; 50% of its full capacity.
Read this if you have multiple 100ah batteries
If you have multiple 100ah batteries, you can connect them in series, parallel, or series-parallel.
Series vs parallel connection:
- Series: This will add up the voltage but the amps will stay the same. 2x 12v 100ah batteries connected in series will be equal to 24v 100ah.
- Parallel: This will add up the amps but the voltage will stage the same. 2x 12v 100ah batteries connected in series will be equal to 12v 200ah.
Series vs parallel connection — which one is best for you? Your first priority should be the series connection. A high-voltage system will increase wiring efficiency. But make sure "your inverter should support 24v input".
If you have a 12v inverter, use a parallel connection but thicker wiring from battery to inverter.
If you have more than 2 batteries, use a series-parallel connection.
Note: To maximize the power, when connecting multiple batteries they should be the same capacity, voltage, brand, and age.
How Long Will A 100ah Battery Last?
How Long Will 100ah Lead-Acid Battery Last?
- 100ah lead acid battery will last anywhere between 20 hours to 1 hour. The exact time will depend on the size of the load.
How Long Will 100ah Lithium (LiFePO4) Battery Last?
- 100ah lithium battery will last anywhere between 50 hours to 30 minutes. The exact value will depend on the size of load.