Charging LiPo Batteries in the Field for FPV Mini Quad

Charging LiPo batteries in the field is an excellent way to let you fly for longer. I will share my field charging solution which I believe is better than buying more LiPo batteries in many aspects.

When I go flying, I can easily go though 20+ batteries in an afternoon with my 5″ mini quad. You can certainly buy as many batteries as you need for a single session. But I find charging in the field a more cost effective and practical solution. In this article I will explain how, and why.

Further Reading: How to choose LiPo batteries for Racing drone

My Field Charging Solution

Equipment

equipment for charging Lipo batteries in the field

My equipment for charging Lipo batteries in the field

How to Charge LiPo Batteries in the Field

Ideally you should have at least 8 batteries for this to work smoothly. You can make it work with fewer batteries, but you might have to spend more time waiting.

I prefer to parallel charge 2 batteries at a time at 2C, it should only take roughly 20 mins to complete. For example for two 4S 1500mAh batteries, I set the charge current to 6A.

It’s a good idea to leave your batteries to rest for at least a few minutes between discharging and charging . This will allow them to cool down and reduce the change of overheat.

8 Batteries Become 18!

Using this equation we can calculate the total watt-hour in a battery.

Energy (Watt-hour) = voltage x capacity

With a 6S 10000mah, you can charge roughly 10x 4S 1500mAh batteries.

25.2 x 10000 / (16.8 x 1500) = 10

So this whole setup is equivalent to having 18x 4S 1500mAh!

High capacity LiPo battery for field charging

High capacity LiPo battery for field charging

Okay, let me explain why I love field charging so much.

Field Charging is Cheaper

You can save money by buying fewer batteries. Using the Acehe Formula 4S 1500mAh ($36) as an example, you could save over 40%!

  • 18x 4S 1500mAh batteries = $648
  • 1x 6S 10000mAh batteries + 8x 4S 1500mAh = $388

Furthermore, you can make the most out of those batteries. LiPo batteries for racing drones have hundreds of cycles. Sometimes we buy so many we don’t use enough cycles to get the value back. The performance of LiPo also gets worse over time even if you don’t use them a lot (Internal resistance increase).

With field charging you will be using 2 to 3 cycles on those batteries instead of just 1 per session.

Flexibility

It’s not a good idea to leave LiPo batteries fully charged for too long for safety and to avoid performance degradation. It’s annoying to still have fully charged batteries left after a session because you need to discharge them if you are not flying any time soon.

Fear no more. With field charging you can “reverse charge” them back to the big battery, or any empty batteries.

“Reverse Charging” – Drain your fully charged LiPo’s; Image credit: Horváth Csaba

You can also share your charging station with your friends. And you can charge other types of battery too such as your FPV Goggles battery.

Portability

The weight of a field charging setup is only slightly lighter than carrying the whole 18 batteries.

  • The weight of 18 small batteries: 3.4Kg
  • The weight of 8 small batteries + 1 big battery + charger + parallel charging board = 1512g + 1210g + 450g = 3.1Kg

The overall weight saving might not be a big deal, but it does take much less space. The 6S 10000mah LiPo is only slightly bigger than four 4S 1500mah.

Field Charging can be Safer

By keeping and charging a smaller number of Lipo batteries in the house, there is a lower chance of fire, statistically speaking.

The Limitations

Field charging might not be everyone’s cup of tea.

  • You need a new LiPo charger, if you don’t already have one that support LiPo input
  • All the arguments are based on the assumption that you fly a lot, e.g. 20 packs or more in a session. If you don’t fly enough then this might be less appealing to you
  • In order to parallel charge, your batteries have to be at similar voltage level. That means you have to pay extra attention to the voltage while flying and decide when you should land. I found this is easier if you have a current sensor, and just monitor how much mAh has been consumed

Choosing a Portable Charger

First of all, you will need a portable charger that can be powered by DC. The input voltage range should be wide enough to support your choice of portable power source.

I particularly like the iSDT series (SC608, Q6, SC620) for charging LiPo batteries in the field because of their compact and light weight designs. They support 9V-32V input and come with an XT60 connector that allows LiPo batteries as power source. They are also great for everyday indoor charging.

Take a look at my LiPo battery charger recommendations.

Choosing Portable Power Supply

To power the charger without access to a wall socket and electricity, you’ll need a portable power source. Here are some common solutions:

Name High Capacity LiPo Batteries Portable Generator Deep-cycle Batteries Solar Generator
Fuel Rechargeable Varies – Petrol/Diesel Rechargeable Rechargeable – Sun
Voltage 11.1V – 25.2V (3S-6S) Varies – AC and DC 12V Varies – AC and DC
Capacity Low (10Ah – 16Ah+) High High (20Ah – 120Ah) Medium
Weight Light (1Kg – 2Kg) Heavy Heavy (5Kg – 35Kg) Medium
Price Cheap Expensive $50 – $300 Expensive
Example
Products
4S 16000mAh
6S 10000mAh
6S 16000mAh
Wen DeepCycle Suaoki

It’s possible to use car battery for charging LiPo, but we don’t recommend it in case you kill it. We recommend using a separately deep cycle battery instead.

If you have a lot of batteries to be recharged in the field, or need to power multiple chargers, a portable generator is a good option. They are powerful and often have DC as well as AC output which is compatible with a wider range of chargers. But generators are noisier and more expensive than other options in our list.

Solar generators are another great option especially for sunny day camping/flying.

I personally prefer the simplicity of a high capacity LiPo battery which I can easily carry in my backpack.

Edit History

  • Jul 2017 – Article created
  • Apr 2018 – Updated info about my own field charging solution and how it compares to buying extra lipo batteries

24 thoughts on “Charging LiPo Batteries in the Field for FPV Mini Quad

  1. Martin Alvarado

    Oscar.
    Can I use a 12v car battery to field charge? Or even a 24 volt.

    Also if my power source is 12 volt car battery. Would I been able to charge 4S lipo batteries? How does that work if 4S is much more than 12 volt.

    Correct me if this statement is wrong. My lipo Charger is capable of 8-36 dc volt input capable. I obtain a 24volt RV or Marine battery. This setup should work.

    Thanks

    Martin

    Reply
    1. Oscar Post author

      Depends on the charger you plan to use. For the iSDT chargers I recommend they should be able to take both 12V as well as 24V.
      Yes you can charge 4S with 12V input, chargers can “step up” the voltage.

      Reply
  2. WhaleFPV

    Hi guys if you field charge you need to go check this new product from rcharlance…

    I’ve just bought 2!
    It has 1 xt60 input for power source (with voltage monitor and alarm) and 2 xt60 outputs

    Banggood £9.48
    banggood.com/Rcharlance-Power-HUB-XT60-2X25V-QC3_0-9V-2A-5V-3A-Power-Adapter-For-Phone-Ipad-XT60-Devices-Charging-p-1336776.html

    Gearbest £7.51
    gearbest.com/charger/pp_009305459141.html
    Thanks for the great info as always Oscar!

    Reply
  3. AnalogKid

    Oscar
    How long would you recommend a 10C battery like the multi star be kept at “near full” or even full charge.
    Ie If it was charged , ready for the weekend, but not used at all; and discharged on a Sunday evening wold that be “OK”.

    I say this as I have a basic understanding (right or wrong) that high C lipos suffer the most when kept at full charge versus low C lipos.

    Reply
    1. Oscar Post author

      It’s hard to say, personally, i wouldn’t worry about it for a week or two. Any longer you might want to put it in storage charge.

      Reply
  4. James

    Why use a 6s battery to charge with instead of 4 or even 3s? Since it’s the mah you’re after here, not the voltage, aren’t the extra cells just taking up space, why would you want more voltage when charging, as opposed to amperage?

    Reply
    1. Oscar Post author

      The energy stored in a battery is a result of voltage and capacity :) so the higher the voltage the more energy you get.

      Reply
  5. Brquad

    Oscar, I’ve been field charging for about a year. I mainly use the battery on my SUV (the charger will shut down when input voltage gets too low. I also have a built-in inverter that I can use also, but either the vehicle must be running or the ignition turned on…

    I have looked at buying a large capacity 6s battery in the past and then just now after reading your article. Where on God’s green earth are you guys buying 6s 160000mah batteries for “cheap”? the lowest price I’ve seen is around $200 from sketchy retailers….

    Reply
    1. Brquad

      My mistake I meant, 6s 16,000mah, but I’d be happy with a 10,000mah suggestion (4s or 6s for under $100)! Thanks

      Reply
      1. Buddah

        Ebay 6s 10k 78$ shipped:

        ebay.com/itm/Turnigy-MultiStar-4S-10000mAh-10C-LIPO-Battery-Pack-XT90-for-eBike-Multirotor/323110548546

  6. Davidoff

    Thats sounds good! I have a skyrc imax b6ac v2 and it has both ac and dc input. Can I use this as a field charger if I buy an xt60 to jack adapter?

    Reply
  7. Azhar

    I bought the 6s 5200mah Multistar for USD22 during a Hobbyking sale for this very purpose. Cheap and small enough capacity in terms of WH to be able to hand carry into a plane (limited to 160Wh and below) if I want to go overseas on a flight.

    6S 10A is just too big.

    Reply
  8. Alex

    How can you estimated the amount of charging a field lipo can do? For example, how many 1500mah 4s packs discharged to 3.6 a cell can a 20000mah lipo bring up to 4.2 a cell?

    Reply
    1. Oscar Post author

      you probably have to try and see, because it largely depends on your charger’s efficiency.
      But as a good estimation, you can use this formula:

      Number of packs = (source voltage) * (source capacity) * 80% / (target voltage) * (target capacity)
      *assuming your charger has roughly 80% efficiency

      In your case, 20Ah*16V*0.8 / 1.5A*16V = 10.7
      so about 10 packs.

      Reply
  9. Slawek

    Oscar, you have mistake in article. 6S battery has more than 50% more energy than 4S battery (with the same capacity). You propablly mean 3S.

    Reply
      1. deadmoo

        You got it backwards. The 0.66 is how much energy 4S has compared 6S. 4S has only 2/3 the energy of the 6S. This is so because the 6S has 50% more, it is 1.5 times the energy of a 4S. Both calculations are correct, just saying it in the opposite order.

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