What Filmmakers Need To Know About Batteries!

Cameras, lights and accessories need batteries for filmmaking. With ever-increasing power requirements, now is a good time for a refresher on Physics Lessons about Principals of Electrical Engineering.

Maximum Watt Hours

Batteries are usually marketed by giving camera operators the maximum Watt Hours they’ll give. Most common ones these days are 98Wh, which usually are easiest to take on a plane then the 150Wh, 200Wh and 300Wh versions. But how important is the maximum watt hour? Most filmmakers will think a high max Wh means longer shooting times, but this isn’t always the case.

Not All Batteries Are Equal

Power = Voltage x Current. If you are choosing a battery for a high load situation such as lighting or a camera with lots of accessories, Maximum Current Draw is what you are looking for. Lithium Ion Batteries are normally marked as 14.4V. They start off around 17V then decrease linearly down to around 11.5V. Remember the good old NiCad Batteries? They gave you max voltage forever, then fell off a cliff. You had to be vigilant, so they didn’t run out whilst you were shooting.

Current Drawn by Cameras Changes

Current requirement changes with the Lithium Ion as the Voltage drops. The higher the load, the quicker the Voltage will drop. Say you had a camera that wanted 100W of power, when you put your nice freshly charged battery on the kits that’s 17V, the Current draw is 5.88A. When the battery Voltage has dropped to 13V it wants 7.69A. Bit of a bummer if the battery is only rated at 6.8A.

To illustrate these points, let’s look at IDX’s batteries. IDX’s CUE-D95 Battery is rated at 91Wh, the IDX DUO-C98 Battery is rated at 96Wh. Not much on the face of it. The CUE-D95 is £140 the DUO-C98 is £245. There are differences between the features of both batteries that are reflected in the cost but let us look at the maximum current draw. The CUE-D95 is 6.3A maximum current draw, the DUO-C98 is 10.5A. With both batteries discharged to 13V the maximum power the CUE-D95 can supply is 82W, but the DUO-C98 can still supply 136W. So, if your requirement is 80W the CUE-D95 is about to bug out; the DUO-C98 can run itself all the way down to 11V when the camera has reached its minimum voltage. The extra 5Wh with the higher max Current equates to around 50% more run time.

So, when you’re looking to buy batteries, consider what you want them for and what the power requirement of the equipment is. Don’t look at Watt Hours on its own. Look at maximum current draw!