An FPV Drone Battery is the foundational component of a quadcopter and must be considerately selected to achieve an ideal balance between performance and flight time. Lithium batteries are the most common battery chemistry used to power quadcopters due to their high energy densities and high discharge capabilities. This article will discuss the differences between various lithium batteries, battery specifications and also provide some basic recommendations. By then end of this article, you should be able to observe and understand any quadcopter battery label and have the information required to make an informed decision when selecting quadcopter batteries.
LiPo and LiHV FPV Drone Battery
The lithium battery packs used to power quadcopters have two common chemistries: Lithium polymer (LiPO) and lithium polymer high voltage (LiHV). The primary difference between the two is that a LiPO cell has a fully charged voltage of 4.2V compared to a LiHV cell which has a voltage of 4.35V at full charge. A LiPO has a resting or nominal voltage of 3.7V versus a LiHV which has a storage voltage of 3.8V. In regards to the performance of the two packs, a LiHV battery will initially provide more power but abruptly drops in voltage when discharged whereas a LiPO has a more linear discharge making it easier to qualitatively gauge the remaining flight time. LiPO packs are the most commonly used across all sizes of quadcopters however LiHV packs are quite popular for use on “Tiny Whoop” micro drones because the extra voltage moderately improves the quadcopters performance.
FPV Drone Battery Cells and Voltages
Battery voltage is the potential energy difference between the positive and negative terminals. A higher FPV Drone Battery voltage allows the pack to provide more power to the quadcopter without increasing the current or amp draw. A standard lithium polymer cell has a nominal (storage) voltage of 3.7V hence to increase the power that a single LiPO pack can deliver, these cells are grouped together in series (meaning the ground/negative lead from the first cell is connected to the positive lead of the next cell, forming a chain of individual cells) to increase the overall battery pack voltage. LiPO packs are commonly sold in 1S, 2S, 3S, 4S, 5S or 6S configurations where the digit followed by the ‘S’ stands for number of cells in that specific pack. The more cells that are grouped together, the more voltage the overall battery pack will have. The battery pack voltage is important as it impacts the maximum motor speed of a quadcopter. This is explained further here [insert hyperlink to the article on motors/ section on KV] but simply, more battery voltage allows the motors to spin with greater speed (RPM). For this reason, 4S LiPO’s are the most commonly used for racing quadcopters as they provide a balance between speed and weight. The following table summarizes the voltage and common applications for various LiPO cell configurations. It is important to note that the quadcopter applications listed in the following table are only typical examples from the many different battery-quadcopter combinations in existence. Exotic setups such as 5S 150mm racing quadcopters or 2S micro brushed quadcopters do exist however they are just quite uncommon.
FPV Drone Battery Capacity
Battery capacity is measured in milliamp hours (mAh) which is a unit describing the current a battery can supply for a unit of time. As an example, a 1500mAh battery would be able to supply: 1500 milliamps (1.5A) of current for an hour, 3000mA (3A) of current for a total of 30 minutes, 6000 mA (6A) for 15 minutes and so on. A higher milliamp rating on a battery essentially means that it will provide more flight time per charge. When choosing a battery, a sacrifice must be made between the battery size and the weight. A larger capacity battery will provide a longer flight times however the added weight will restrict the performance of the quadcopter by increasing the craft’s momentum thereby making it respond in a more sluggish manner. In racing scenarios, the usual selected battery capacities for a 220 sized quadcopter range from 1000mAh to 1500mAh with 1300mAh packs being the most common. On average, a 1300mAh 4S pack will last for about three minutes in a racing quadcopter although flight time is entirely dependent on the manner in which the craft is flown. A professional racing pilot can easily discharge a 1300mAh 4S pack in under two minutes compared to a slower flying beginner who may experience up to five minutes of flight time with a similar battery. When flying longer or faster circuits, many professional race pilots will actually switch from a 1300mAh 4S pack to a heavier 1500mAh battery to reduce the need for battery voltage management during a race. In order to achieve increased flight times(5-8 minutes), long range quadcopter pilots will use even larger batteries up to 2200mAh as flight performance is of less regard to them than flight time.
FPV Drone Battery C-Rating
The C-Rating of a battery is a unit of measurement dictating how much current a battery can continuously supply for its given charge cycle. Simply put, the higher the C-Rating of a battery, the more current the pack can continuously supply. The C-Rating can be multiplied by a batteries capacity in order to calculate a packs theoretical maximum discharge current. Larger capacity batteries can usually supply more current as their internal electrodes have a greater surface area. For example, using the below C-Rating and milliamp conversion formulae, a 1800mAh 100C battery would be able to supply more current to a quadcopter than a 1300mAh 100C battery (180,000mA/180A maximum current versus 130,000mA/130A maximum current respectively). If a battery is forced to supply more current than dictated by its C-Rating for a significant period of time, it can damage the battery by causing the cells to puff, reduce overall longevity, cause excess heating and occasionally cause a LiPO fire. For this reason, it is important to use batteries with C-Ratings that are adequate for their application. For most 220 sized quadcopters, batteries with C-Ratings of 70C or higher are usually recommended, however, quadcopters using high KV and/or large motors may require even higher C-Rating batteries.
C-Rating Formula: Maximum Safe Current Draw (mA) = Battery Capacity (mAh) * C-Rating
Milliamp Hour Conversion Formula: 1000mA=1A (one amp is one thousand milliamps)
Another use for the C-Rating formula is to calculate the compatibility between different motors, propellers, electronic speed controllers (ESC’s) and batteries. As an example, a 1300mAh 100C battery would have a safe continuous current draw of 130A (130,000mA). Dividing this number by four (as a quadcopter has four motors) it is apparent that 32.5A is the maximum current draw per motor that this battery can continuously supply. ESC’s can then be chosen accordingly to accommodate the maximum continuous current draw (in this case a 30-35A ESC would be the most suitable). As a generalisation, most batteries can temporarily exceed their rated continuous current draw safely for around ten seconds. This means that a motor-propeller combination is suitable for use with a battery if the average motor amp draw is within the calculated maximum continuous current draw per motor. It is safe to assume that for most flights, the average throttle position will be at a maximum of 75%. Using this logic, a motor-propeller combination will, on average, be suitable for use on a quadcopter if 75% of the maximum motor current draw is below the calculated maximum continuous current draw per motor. Going back to the current example, a motor-propeller combination quoted with a maximum current draw of e.g. 40A would actually be suitable for use with the 1300mAh 100C battery as the average current draw from that motor would be 30A (0.75 * 40A) which is below the calculated maximum continuous current draw per motor of 32.5A. The website: https://www.miniquadtestbench.com/ is a useful resource when performing these calculations as it provides data comparing the maximum current draw and thrust for many different motor and propeller combinations.
FPV Drone Battery Connectors
There are a whole series of available LiPO battery connectors. The most common connector is the yellow XT60 which is used on about 95% of 220mm sized quadcopters running a 3S-6S LiPO FPV Drone Battery. Micro drones such as the Tiny Whoop commonly use the JST-XH as it provides more current flow from the battery compared to the smaller JST-PH. The following table summarizes the most commonly used battery connectors:
LiPO batteries (except in the case of a 1S) will also have a balance lead. This is a standard JST-XH connector with 3-7 pins that is used to balance charge the battery pack. More information on balance charging can be found here. This connector has one positive pin for every cell in the battery pack and a ground wire (usually black). A battery checker can be plugged into this connector to monitor the voltage of each individual LiPO cell, simplifying the process of distinguishing charged and discharged batteries.
The danger of LiPO batteries is something that many people underestimate but should not be overlooked. Lithium batteries store large quantities of energy in a small profile and are occasionally prone to catching fire. This is a rare scenario and is most likely to occur when charging, discharging, or if a battery becomes damaged. Regardless of the odds, a LiPO fire can result in houses burning down, self-injury or damage to gear. For this reason, it is essential for all pilots to store and ideally charge their quadcopters lithium batteries in a fire-proof LiPO bag or box. If you have already spent a few hundred dollars on FPV gear, what is a few more to potentially save a lot more in damage.
FPV Drone Battery Disposal
LiPO batteries are disposable items with a limited lifespan of around 150-250 cycles (Battery University 2017) although this number is entirely dependent on the manner in which they are looked after and used. The main factors impacting the longevity of a LiPO are over-discharging and leaving packs in a charged/discharged state for long periods of time. To increase the longevity of a LiPO, it is recommended to store LiPO batteries at 3.8V per cell and to land a quadcopter at a minimum of around 3.5V per cell (although landing at 3.65V per cell is the safest option). When the LiPO is nearing the end of its life cycle, large voltage drops will be noticeable on throttle punches as the quad will fail to quickly speed up the motors. The LiPO will also lose an increasing percentage of its capacity meaning reduced flight times. To properly dispose of a LiPO, the safest option is to first discharge the pack using a battery charger and then to connect the power leads to a 12V incandescent light bulb for several hours. This will ensure that the LiPO is fully discharged to 0V. As entertaining as the fireball looks, it is not wise to dispose of a LiPO by puncturing or damaging it. Once the LiPO has been discharged completely, it is ideal to cover over the battery terminals and take the pack to your nearest battery recycling facility in order to reduce the overall environmental impact (Battery University 2017).
Who Plugged In?
On a final note, when at a race meet or flying with other pilots, it is common FPV etiquette to leave your quadcopter batteries disconnected from the craft whilst other pilots are in the air. This prevents a scenario where a pilot is blasted out of the air by your video transmitter powering up and makes the event run a lot more smoothly.