If you have a drone, sooner or later you’re going to want to charge your drone battery off-grid. The problem is that drones use big batteries, so to charge a big battery you need an even bigger battery – a simple solar panel USB charger might be good enough to charge your phone, but it isn’t going to provide enough current to charge a drone battery. There are a few commercial options available that can charge your drone batteries without an AC outlet, but I decided to build my own…(spoiler – don’t bother!)
To compare apples to apples (or batteries to batteries), we need to convert the capacity of a battery from the usual milliampere hour (mAh) list ratings to watt hours (Wh). Milliampere hour (mAh) battery capacity is dependent on the voltage used, whereas watt hours (Wh) are the amount of energy the battery will provide over one hour (when the voltage is known).
The calculation is pretty simple: the formula is (mAh)*(V)/1000 = (Wh). The nominal operating voltage for lithium ion-batteries is usually 3.7 volts – so we will use that for our calculations. The Mavic’s battery is rated at 43.6 Wh (3830mAh rating x 11.4 operating voltage / 1000). However, since your Mavic will usually return home with a 30% charge left over, you will never have to fully charge the battery – just the 70% of the battery that was used in the flight, or approximately 30.5 Wh. This is important for two reasons. First – your input voltage must be in that range or the charger will not charge the battery. Second, you need an input source that can discharge 6A worth of juice – that is a lot of power and far beyond the capacity of most portable solar panels or small wind turbines. (In comparison, USB chargers deliver 5V at just 2A or less). It is possible to use an inverter to step up a DC input source to AC and plug in your regular AC drone battery charger, but this involves a lot of inefficiency (and some issues with voltage as we will discuss). Whenever possible, it is preferable to work with a DC-DC charging system. Finally, before you decide what you need to charge your drone batteries off-grid, you need to consider your specific needs. Do you just want to get a couple extra flights in, or are you looking for multiple charges over a long period of time?
Commercial Options for Charging Drone Batteries Off-Grid
If you’re going on an extended trip beyond the reach of civilization, you will need something with a really big battery and a large enough solar panel to charge that really big battery. Goal Zero Sherpa 100
DroneMax M10
The battery in the DroneMax M10 is rated at 99Wh so theoretically you might get slightly more than two charges out of it if you are starting from a battery that is only 70% depleted.
Semi-DIY Option for Charging Drone Batteries Off-Grid
If you’re only going to be away from an AC outlet for a few days and you are only looking to get one extra flight, a much simpler and cheaper option is to just bring a fully charged high capacity battery with you. Here are two options that will work to charge your drone battery for at least one extra flight: 90 Wh Laptop Travel Charger Power Bank
It’s small and only weighs 624 grams (about 1.4 pounds) and comes with a built in AC inverter so you can directly plug it into your normal AC drone battery charger. The downside is that it doesn’t have direct 12V DC out, so you’re losing efficiency by stepping up the output from this battery to AC and then back down to DC to charge your drone battery – so even though it has a 90Wh capacity, it’s doubtful that you’ll get more than a single full charge out of it. $100 is still a little pricey too, compared to the cost of another flight battery. 130Wh Portable Battery Power Bank
This battery can be charged with a micro-usb, so if you are really off the grid you can charge this battery with a solar panel charger (although that is likely not very practical because it will take a very very very long time). The only problem if you are trying to charge a Mavic is that the DC output port is limited to 4 amps, which may be below the minimum input current threshold for the Mavic’s battery (I haven’t tried this specific battery so I don’t know for sure). 18000mAh Portable Car Jump Starter
This battery is also small and light weight (listed at 500g or 1.1 pounds). It has less capacity but is quite a bit less expensive than the first option. Although this battery is designed as a portable car jump starter with a 12V/300A jumping port, it also has a regular 12DC output port, so you can charge your drone batteries DC to DC without an inverter using a car charger. I have tried a similar car battery jump starter and even with 70 Wh of juice, I barely got one single charge. And if you’re wondering, you can connect your drone car battery charger directly to the 12V/300A car battery jumper leads – in case you’re looking at a battery that doesn’t have a 12V output port. Again, the cost doesn’t justify the purpose – for $70 you might as well just buy another drone battery.
DIY Option for Charging Drone Batteries Off-Grid
After realizing that I really only need some form of high capacity rechargeable battery to take with me to charge my drone batteries off grid, I started looking around the house to see what types of high capacity batteries I already own. As it turns out, you probably own more than a few high capacity rechargeable batteries that you could adapt to charge your drone batteries without an AC outlet in the field. Uninterruptible Power Supply
It’s not very portable, or practical – but if it can run your computer you can get one or two drone battery charges out of it. Lead Acid Battery
As the name suggests lead acid batteries are heavy – but they’re cheap, rechargeable and have the juice to charge your drone batteries. Maybe you have a spare from your ATV, boat or snowmobile sitting around in your garage right now. Strobe Battery Do you use a strobe with a battery power pack? If yes, then you have a high capacity battery that you could theoretically use to charge your drone batteries.
I use Elinchrom Quadra strobes which use a pretty big lithium ion battery (the new Elinchrom batteries above are listed at 90Wh and 144Wh respectively). Depending on what strobe system you use, it probably wouldn’t take much to build an adapter for these types of batteries to provide the 12V DC out needed to power a drone battery charger. The problem is that they are really expensive and complex (I took one apart to see if there was a simple battery cell in there – there isn’t, there are lots of cells individually connected to a circuit board) – so for me, not worth screwing with. AA Battery Bank I own a lot of rechargable AA batteries. Nickel Metal Hydride batteries are not nearly as light weight as an equivalent lithium-ion battery, but they are still a rechargeable power source than can be used to create as big of a battery array as you want (click here for more technical information). The problem is that it takes ten 1.2V rechargeable AA batteries connected together in series to make a single 12V battery bank, and the capacity of the resulting battery is limited to the capacity of the lowest rated individual cell. In my case I have lots of Sanyo Eneloop XX batteries. Each battery has a rating of 2400mAh – so ten of them together produces a single 12V 29Wh, 2400mAh battery. In order power the drone battery charger (direct DC) at least three 10 battery arrays have to be connected in parallel (30 AA batteries in total) – resulting in a single 12V, 86Wh, 7200mAh battery.
I bench tested this setup with four x ten battery arrays (40 AA batteries in total) for a AA nickel metal hydride battery with a theoretical capacity of 12V, 115Wh, 9600mAh – with a direct DC to DC charger connection. Starting off with forty fully charged AA Sanyo Eneloop XX batteries with a direct DC to DC charger connection I was able to charge a 70% depleted drone battery only 1.25 times. As you are probably realizing, AA nickel metal hydride batteries are not nearly as efficient as high capacity lithium-ion batteries – this is starting to sound a lot like the Mercedes AA Class!
Conclusion
After bench testing several high capacity batteries and trying to build my own AA battery array, I could not get more than about one and a half drone battery charges out of any of these setups. The main problem seemed to be that the DJI car charger has an input voltage of 12-16V and 6A of current is required to charge a Mavic battery. No matter what I tried I could not get the the charging battery voltage to stay above the 12V cut off voltage of the charger long enough to charge more than one and a half drone batteries from 70%, even though all of the larger batteries I tried should have had plenty of capacity for at least two charges. Testing with the AA battery array proved that 10 fully charged Sanyo Eneloop XX batteries produce an output of 13.72V. 11 gives 15.52 and 12 produces 16.73. I tried starting with 11 AA batteries (12 was over the maximum charger input voltage of 16V) and then adding an extra AA battery into each of the 12V cells in the array once the voltage dropped – but it didn’t matter – there was only enough current to charge the drone battery at most 1.25 times. My overall conclusion is that it’s not worth dragging around a much larger and heavier charging battery just to get an extra flight and a bit – it is far more economical and practical to simply buy more drone batteries. This isn’t the answer I was hoping for – but unless you happen to have one of the batteries listed above sitting around the house for another reason – and size and weight are not an issue – hey you can probably get at least one extra flight out of it. Essentially your choice comes down to economics and practicality. Is is cheaper to buy a bigger battery to charge your drone’s batteries off-grid? Not really. Is it easier to pack and carry a bigger battery instead of multiple smaller drone batteries? Probably not.
How Do You Charge Your Drone Battery Off The Grid?
These are all the options I could come up with the charge drone batteries off the grid – but I’m really curious to know if anyone has found a better solution. Has anyone tried a really big solar panel? What about portable options besides a battery – a peddle alternator or something like that? Has anyone figured out a way to trickle charge a high capacity drone battery? Or have you had more success than me charging your drone batteries with other batteries? Leave a comment below and let us know.
