How to Calculate Approximate Runtime of an LED Battery
Ever had an LED studio light fixture go out sooner than you expected in the middle of a shoot, and wondered “Wait, shouldn’t this battery have lasted longer?”. The good news is that calculating how long a battery will approximately last for is easier than you might think. With just a few key numbers, you can get a rough idea of your battery’s runtime.
Whilst this calculation can only provide an estimate, as other factors can affect battery runtimes (which we will get into a bit later), it is a great starting point to give you a rough idea for that extra bit of reassurance, especially on an important shoot.
The Formula (Not as Scary as you think, Promise)
To get a rough estimate of how long your light will last for using a particular battery, all you need to do is follow these steps:
Find your numbers:
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Look at your battery’s capacity. It’s usually written on the battery itself in Wh (watt-hours).
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Look at your light’s power consumption. Usually written in W (watts).
Do some quick division (we even let you use a calculator):
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Formula: Battery capacity ÷ Light power = Runtime in hours
Example:
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Battery Capacity: 99 Wh
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Light Power: 150 W
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How to Calculate: 99 ÷ 150 = 0.66 hours
Convert to minutes (optional):
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Multiply by 60.
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0.66 × 60 ≈ 40 minutes
What if My battery doesn’t have a Wh Rating on it?
If your battery doesn’t have the Wh rating printed on it, then all is no lost, you can still work it out by following these steps:
Check your battery label:
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Sometimes it shows Wh (watt-hours) directly (in which case you don’t need to worry about the following steps).
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If not, look for either mAh (milliamp-hours) or Ah (amp-hours) along with the Voltage (V).
If you see mAh and Volts:
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Use this formula: (mAh × Volts) ÷ 1000 = Wh
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Example: (6,900 mAh × 14.4 V) ÷ 1000 = 99.36 Wh (≈ 99 Wh)
If you see Ah and Volts:
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Use this formula: Ah × Volts = Wh
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Example: 6.9 Ah × 14.4 V = 99.36 Wh (≈ 99 Wh)
Now you know how to calculate your battery’s watt-hour rating, even if it’s not printed on the battery itself.
Things to be aware of:
While these formulas can give you a rough estimation of how long your battery might last, they aren’t foolproof. Several other factors can affect actual runtimes, so it’s important to keep them in mind.
Here are a few key considerations:
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Voltage Compatibility: A 99Wh battery at 14.8V might seem sufficient, but if your light requires 24V or higher, it won’t work without a step-up converter or dual battery plate. Always check your light fixture’s voltage requirements before buying a battery.
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Current Draw Limits: Even if a battery’s capacity (Wh) is enough, its maximum discharge current can limit what devices it can safely power. For example, a 150W load at 14.8V draws about 10A (150 ÷ 14.8). Make sure your battery can handle this continuous load.
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Efficiency Losses: In practice, energy losses from DC-DC conversion, regulators, and cabling can reduce usable runtime by 10–15%. So instead of 40 minutes, you might only get around 33–36 minutes.
Please keep these quirks in mind, and your battery won’t let you down when it matters most.
We hope this guide has made it easier to understand how long your battery can power your studio light fixture for. While estimating battery life isn’t an exact science, the tips and formulas shared here should give you a good idea of what to expect. Armed with this knowledge, you’ll be better equipped to make informed decisions when selecting your next rechargeable battery pack, so you won’t literally get left in the dark.
Godox is a world-renowned brand & leading manufacturer for professional studio lighting equipment. Renowned for their high quality and innovative products, they lead the Film, TV and Photography industries with professional lighting.
EssentialPhoto & Video is the Official Godox Partner and UK Distributor, stocking the widest range of Godox kit in the UK, offering a 12 Month Warranty*, and Customer Support and after-sales repair at our Birmingham-based store. All Godox stock is dispatched from our warehouse in the West Midlands, UK.
