Trevor Wichmann
Senior Director of UAS Ops Consulting at Skyward

Drones are becoming common on construction sites at every phase of a project, from design to inspection. When an increasing number of drones performing an increasing number of tasks, logistical concerns become amplified.  What can be a minor inconvenience when you’re using just a few drones can become a major bottleneck as you begin to scale.  

A few weeks ago, members of the Skyward team met with a dozen major construction companies at the Verizon Innovation Center in San Francisco. When we compared notes afterward, we realized that we had all heard the same question over and over: How should we be managing our batteries?

There are questions about safety, logistics, storage, and it’s not always easy to find straightforward answers. Here are five tips to keep in mind when planning your battery logistics.

1. Safe Drone Battery Storage Is Crucial

Lithium-ion and lithium-polymer batteries can be highly combustible when punctured, overcharged, or otherwise mishandled. When the battery is damaged it produces heat and gas, and a single damaged cell can, in some cases, rapidly produce a violent chain reaction.

Proper handling procedures can help mitigate these risks. Best practices are easier to uphold in a controlled facility, but it can be difficult to maintain the same kind of environment on a construction site where equipment is more exposed to the elements and space is at a premium. Even when it’s inconvenient, make sure never to compromise the safety of your batteries, especially during charging and discharging. Here are some rules to keep in mind:

  • Charging and discharging are particularly dangerous processes, and both should be done under observation.
  • To prevent fire, ensure that there are no flammable materials within five feet of the charging station.
  • The storage facility should be cool, dry, and equipped with a functioning smoke detector and fire extinguisher. If you are charging outdoors, keep the batteries out of direct sunlight.
  • When storing LiPo batteries for more than 24 hours, be sure to discharge them to 50 percent or less if the battery is not equipped with protection circuitry.

2. How Many Drone Batteries Should You Have on a Construction Site?

We get this question all the time, and naturally there are a lot of variables to consider. Some use cases, like creating a 3D model of a completed structure, will likely require more juice than straightforward 2D imaging of a job site—though this depends on the size of the flight area and other factors.

Here’s what Tariq Rashid, Skyward’s chief pilot, recommends: For an aircraft that uses one battery at a time, four batteries per aircraft is an absolute minimum for a commercial operator. Six batteries per aircraft may be acceptable if you can easily move batteries from one aircraft to another or charge in the field to meet surges. If it’s not easy to shift batteries between aircraft or charge in the field, you will need eight batteries per aircraft to cover 90% of use cases. 12 batteries per aircraft will likely cover 99% of use cases.

So how did we land on these numbers? From observations of our clients and our own experience, our recommendation is that at minimum you should have enough batteries to fly a total of 45 minutes without having to recharge.

Forty-five minutes is a lot of flying on one job. You can map almost 200 acres at 1 in/px in 45 minutes. If you need to map a larger area than that, you should probably be using a fixed-wing UAS. To reduce anxiety, up the minimum by 15 minutes to one hour. For example, with a Phantom 4, which uses one battery, you should have a minimum of four batteries per aircraft.

Yes, the published endurance of the Phantom 4 is more than 15 minutes, but that number assumes optimum conditions and no reserve. If you need to stay out in the field for an extended period without having to recharge, assuming six planned flights during that period, you will need 8 batteries per aircraft.

For example, a construction company UAS operator would probably not need more than four batteries 50% of the time. About 30% of the time they would need eight batteries. They would need 12 batteries perhaps 10% of the time. This works out to about six or seven batteries per aircraft distributed across the fleet. If your aircraft are geographically isolated from one another and batteries cannot easily be shifted to cover surges, eight per aircraft should cover 90% of use cases. You may have unique requirements that vary from this rule-of-thumb.

Incidentally, being able to shift batteries to cover surges is one of several reasons why some companies have chosen to invest in a single model of aircraft for the entire fleet.

3. Regular Maintenance Avoids Accidents and Saves Money

With a large fleet of drones comes an even larger stock of batteries, and performing usage and condition tracking on both is vital. An accident or job failure is the last thing you want on a construction site, and a battery malfunction can spell disaster. It’s important to note that drones can actually make your job site safer, but they’re only as reliable as their sole power source. Even if you have insurance and nobody is injured, you’d still set back your firm’s drone program, tarnish your safety record, and make it more difficult to apply for waivers from the FAA.

In that kind of worst-case scenario, replacing a damaged drone becomes the least of your worries in the event of an equipment failure. If you want to keep your job site running smoothly and safely, here are some factors to consider before you fly:

  • Is the battery firmware up to date?
  • Which aircraft is each battery compatible with?
  • Are there any external indications of damage?
  • Did an operator have a problem with a battery?
  • Was it involved in an accident?
  • Are you balancing the usage burden between batteries (recommended) or do you prefer to consume the useful life of a smaller set of batteries and replace them sooner?
  • How many charge-discharge cycles has it undergone?

Tracking this data may help you detect a problem with the battery before it causes an accident or job failure. By rotating which batteries you use, you’ll be able to spread the wear and tear over a larger set of equipment, reducing the chance that a battery will fail from overuse.

Skyward provides tools that businesses use to manage and share information about batteries in a clean, easy format. Skyward also offers Take Flight, a comprehensive resource for general operating procedures, including more detailed information on how to handle batteries.

Having a robust system of record like Skyward to manage your entire operation gives managers, legal teams, and other stakeholders insight into the entire operation. And it can help lower drone insurance premiums.

4. Transporting Drone Batteries on Commercial Airlines 

News stories about exploding Galaxy Note 7 phones prompted the FAA and the DOT to ban them from all flights. Though your drone’s lithium ion or lithium polymer propulsion batteries do not contain the same manufacturing flaw that led to Samsung’s debacle, there are still safety restrictions on how LiPo batteries must be transported on commercial flights:

  • They cannot be checked in the cargo hold of the plane, and must be carried on with your personal luggage.
  • If a battery is rated at more than 100 watt-hours (Wh), and less than 160 Wh, each passenger is allowed to carry only two in their carry-on luggage — batteries less than 100 Wh face no such number limit, though.
  • Though it’s only legally required for shipment of LiPo batteries, when traveling by air you should pack your batteries in a puncture-proof container and discharge them below 30 percent. Some people recommend covering the terminals (with tape, for instance) to avoid forming an accidental circuit.
  • Finally, when flying outside the United States, you should make sure to comply with international regulations.

Take a lesson from Richard Lopez of Hensel Phelps, one of the largest general contractors in the country. “Our key has been to keep everything consistent. We all use the same DJI airframes and sensors,” Richard said. “Transporting batteries gets expensive, so each of our district offices needs to have them onsite. We can take aircraft with us if we fly somewhere but not the batteries.”

If you’re at a major firm with numerous locations, and you run your drone operations out of a few different offices, it might make more sense to have drone batteries at offices around the country. This allows the company to avoid the risks, expenses, and hassles of bringing potentially hazardous materials onto a flight, and lessens the need for investing heavily in carrying cases and other supporting equipment.

5. Best Processes Age Better Than Technology

New battery technology is in development, but whatever form the new batteries take, it will likely be years before they’re ready for use on the construction site. We should get comfortable using lithium-ion and lithium polymer batteries because, like it or not, they’re going to be here for a while. Regardless, your stock of batteries will eventually become obsolete, and you will need to either buy upgrades to the batteries themselves or to your fleet. This is one hidden cost of updating your aircraft, and it’s difficult to avoid.

Even though you will eventually swap out the batteries themselves, or their chargers, a well-designed set of procedures will stand the test of time. Even if, as we hope, the new generation of battery technology does not carry the same risks of combustion, and they have larger capacities that make carrying multiple batteries unnecessary, they will still likely have their own safety issues that will need to be addressed—and a construction firm that’s been taking their battery management seriously will be in a better position to meet the demands of the new technology.

The culture of accountability and safety will pay its own dividends, and if you’re using Skyward to manage your ops, it’s simple to incorporate new devices as they come along.

For a more complete set of resources, including a comprehensive general operating manual and standard operating procedures, Skyward offers Take Flight. If you’d like to improve the safety and efficiency of your drone operations, using the documents and checklists offered in Take Flight as a foundation will do just that.