Our research indicates that aerial drone batteries need to be replaced every two to four years. This article will explain our reasoning, which may serve as guidance for your operations. For reference, we fly DJI Mavic and Phantom drones, but other drones that use Lithium Polymer technology will have similar performance characteristics.
Do You Trust Everything You Read on the Internet?
So, I go online and the first page or so of Google Search hits tell me that my DJI drone battery will last up to 30 minutes, can take 200 to 400 charge cycles, and last around two years. Well, that hasn’t quite been our experience, so we’re going to present some information that may more accurately reflect the performance you can expect.
Data From Our Flight Logs Paints a Different Picture
First of all, our flight operations are almost all commercial, primarily supporting the real estate sales and housing development markets. So, our batteries are often required to support flights at altitudes of 400 feet and speeds of 32 mph. This is a bit more demanding than flying at low altitudes and slow speeds. Thus, we shouldn’t expect our batteries to last 30 minutes. So, what should we expect?
We keep log sheets for all of our drone flights, where four years of data shows us:
1. Our average flight times are 18 minutes.
2. Our average battery usage ranges from 96% at beginning to 26% at end (70% diff.).
3. For an average battery usage of 70%, we get about 3.9% per minute. (This is the same as 0.26 minutes per %, just invert.)
This information alone is probably worth your time to read to this point. However, it gets more interesting when the data is examined.
Graphing the Data Reveals Insight into When Your Batteries Need Replacement
The above graph shows that over time your batteries lose their ability to hold a charge. (Our measure of performance is flight time divided by percent battery usage). Microsoft Excel’s trend line tells us the battery’s capacity is around 0.28 minutes per percent (min/%) for a new Phantom 4 Intelligent Flight Battery. At four years, the battery’s capacity has decreased to around 0.23 min/%. This decay appears linearly related to time (not frequency of use) and for the Phantom 4 battery it indicates a 20% loss at four years.
Note the graph shows a 14-month period of no data – but the slope continued linearly indicating it’s the battery chemistry, not usage, that was driving the decay of capacity.
Key takeaway: Your typical 70% flight on day one will last about 20 minutes, and four years later will last about 16 minutes. (There are a number of factors that also contribute to battery performance including deep discharge cycles, damage from crashes, temperatures, etc.)
Mavic 2 batteries had similar graphs and similar flight times, with one important difference. The slope of their decay line was about twice that of the Phantom 4 batteries. The data analysis showed Mavic 2 batteries decay to 80% capacity at around their two-year point.
How does this Information Compare to Performance Specs on the Internet?
We believe this information is complementary to DJI’s performance spec. If you pop your drone up ten feet and let it idle, a new battery may last 30 minutes. But in more demanding situations (read real-world usage), we believe our data more closely represents your experience.
Our commercial flights have been spread across a number of batteries, so each one has a limited number of discharge cycles (less than 100). If you’re usage is significantly higher, then your batteries may lose their ability to hold a full charge at the 300-500 cycle mark, whenever that may occur. According to DJI, that may occur at its two-year mark.
Battery performance depends on its chemistry, which decays over time. We have shown that our Phantom 4 batteries decayed to their 80% capacity point at four years.
Data also shows our Mavic 2 batteries were at their 80% capacity point at two years. We suspect DJI traded off capacity for performance, probably by recalibrating their battery chemistry.
In addition, an aging battery gives off gases, which causes its case to swell. When your battery swells to the point that it requires effort to insert/remove from your drone, this also indicates it’s time to replace. In our experience, our Phantom 4 batteries were sufficiently swollen to warrant replacement at 4 years. Coincidentally, at their 80% point.