How Long Will a 70Ah Battery Last? + Calculator

How long will a 70ah battery last running a DC or AC load will depend on a few factors which I’m gonna share with you in this post.

Need an easy solution? use our battery runtime calculator ( given below ) and Enter the battery specs and the total load in watts to find out how long will a 70ah battery last

70ah Battery Runtime Calculator

Battery Capacity
Ah
Battery Volts
V
Select Battery Type
Load Connected with inverter?
Total Load (watts)
Wh

Note! use my solar panel size calculator to find out what size solar panel you need to recharge your battery in desired hours with solar panels.

Assumptions:

  • Inverter Efficiency: 90%
  • Lead-acid battery: 50% depth of discharge limit
  • Lithium (LiFePO4): 100% depth of discharge limit

Battery Depth of discharge DoD: is the percentage of the battery that has been discharged relative to the total battery capacity. The recommended depth of discharge limit for lead-acid, AGM, and gel batteries is about 50%. Only lithium (LiFePO4) batteries can be fully discharged to 100%.

How To Use The Calculator

  • Enter the battery capacity in amp-hours (Ah): in this case, it’ll be 70
  • Enter the battery voltage: is this a 12, 24, or 48-volt battery?
  • Select the battery type:  Select “Lead-acid” if you’re using a flooded or sealed (AGM or gel) lead acid battery. Select “Lithium (LiFePO4)” if you use a lithium-iron-phosphate battery.
  • load Connected with inverter?: Are you using an inverter to run the load or is the load connected directly through the battery?
  • Enter total load in watts: Enter the total load in watts (e.g 100 for 100 watts of output load)

After entering the information, click “Calculate” button to find out how long the battery last running a load.

if you’ve got some time keep reading… I’ll share a manual calculation method that you can use in the future to calculate any size battery runtime on any load and also some additional information about batteries that will affect the battery last time.

Example

let’s suppose you have a 12v 70ah lead-acid battery (with a 50% DoD limit) and a 400-watt AC load connected to the battery.

How Long Will a 70Ah Battery Last

12v 70ah lead-acid battery will last about an hour running a 400 watt AC load.

Video – Solar batteries 101 (Must watch!)

Must watch this video to understand the basics of batteries (capacity, charge, and discharge mechanism)

Steps to calculate 70ah battery runtime

Follow these steps to calculate the battery life/runtime while running a load.

Steps

1- Converter battery ah into watt-hours (Wh). to calculate the battery capacity in watt-hours use this formula

Battery capacity in watt-hours = Battery amp-hours (Ah) * Battery Volts 

let’s say you have a 12v 70ah battery

70ah battery in watts = 70 * 12 = 840 watt-hours 

2- Multiply the battery watt-hours by the battery depth of discharge limit. ( Default battery depth of discharge limit, Lead-acid battery: 50% DoD limit; Lithium: 100% DoD limit ). Let’s say you have a lead-acid type battery

Battery capacity in wh after DoD limit = 840 * 50% = 420wh

3- Multiply the battery capacity after the DoD limit with the inverter efficiency rate to calculate the AC watt-hours ( Most of the inverters are about 90% efficient)

Battery AC watts = 420 * 90% = 378 AC watt-hours 

4- Divide the battery AC watt-hours by the total load connected. Let’s say 400-watt appliance is connected to your 70ah battery

70ah battery runtime on 400w appliance = 378 / 400 = 0.94 hours

How long will a 70ah battery last? – chart

Here’s a chart on how long will a 12v 70ah battery will last while running a different home appliances.

ApplianceWattage consumptionHow long will a 70ah lead-acid battery last
Fridge300 watts1.2 hours
TV60 watts6.3 hours
Trolling motor720 watts33 minutes
Ceiling Fan120 watts3.1 hours
Computer300 watts1.2 hours
LED Bulb20 watts19 hours
Dishwasher1800 watts12 minutes
Toasters1200 watts19 minutes
How long will a 50ah battery last?

Summary

  • 70ah battery will last anywhere between 6 hours to 12 minutes while running house appliances. The exact value will depend on the wattage consumption of appliance.

Assumptions & Shortcomings of All These Methods

Here are some extra yet important points to keep in mind when figuring out how long will your 70ah battery will last running a load

Battery life cycle count:

  • The storage capacity of the battery will decrease with every cycle ( a cycle is when you charge and discharge the battery to its DoD limit ).
  • 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 )

70ah lead-acid Batteries are rated for 3.5 amps over 20 hours of time:

  • Especially lead-acid type batteries are designed to be discharged at 20 hours. ( means 70ah lead-acid batteries are recommended to be discharged @ 3.5 amps in order to maintain the battery health and reduce the discharge efficiency ).
  • on the other hand, AGM and lithium (LiFePO4) can be discharged at 50% of their capacity.
  • Discharging your battery at a higher rate will increase heat in the battery’s internal cells which will cause power loss. (this factor isn’t included in my above-given methods).
  • For example, if you discharge your lead-acid battery with 70 amps then it’s will not last 30 minutes ( keep in mind the 50% DoD limit ). but it may last about 15-20 minutes.
  • Check the battery discharge rate on the specs sheet of your battery or it’ll be mentioned on the battery (1h → 1C, 2h → 0.5C, 5h → 0.2C, etc.)

Related FAQ’s

How many watts is a 70Ah battery?

70ah battery is equal to 840 watt @ 12v, 1680 watt @ 24v, 3360 watt @ 48v,

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I'm an experienced Sales Consultant with a demonstrated history of working in the renewables and environment industry. Skilled in Photography, Customer Service, and Sales.

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