To have a good flight time and high performance it is important to know how to choose the best Lipo battery. Like most components of a drone, they are related to other components and the battery is no exception . The battery depends mainly on the size of your drone and the type and number of motors used.

Battery voltage and cell count (S)

LiPo batteries used in RC are made up of individual cells connected in series . Each cell has a nominal voltage of 3.7V . Therefore, battery voltage is often referred to by the number of cells in the battery (i.e. "S").

1S = 1 cell = 3.7V
2S = 2 cells = 7.4V
3S = 3 cells = 11.1V
4S = 4 cells = 14.8V
5S = 5 cells = 18.5V
6S = 6 cells = 22.2V

Voltage directly affects brushless motors RPM, so you can use higher cell count batteries to increase the speed of your quadcopter if your motor and ESC support higher voltage[/vc_column_text][vc_column_text]But a battery with more cells of the same capacity is heavier because it contains more cells. To make a 4S 1000mAh battery, you just need to combine two 2S 1000mah or one 3S 1000mah with 1S 1000mah.

The nominal voltage for a LiPo battery is 3.7V. However, that is not the voltage of the battery when fully charged or fully discharged. The number comes from the manufacturers, and is about in the middle of the safe voltage range, so I guess that makes sense.

LiPo battery is designed to operate in a safe voltage range, from 3V to 4.2V . Discharging below 3V may cause irreversible performance loss and even damage to the battery. Overcharging above 4.2V may be dangerous and eventually cause a fire.

However, it is advisable to stop discharging when it reaches 3.5V for battery health reasons. For example for a 3S Lipo, the maximum voltage is 12.6V, and you should stop when the voltage reaches 10.5V (at 3.5V per cell).

LiPo Battery Capacity and Size

The capacity of a LiPo battery is measured in mAh (milli-amp hours). " MAh " is basically an indication of how much current you can draw from the battery for an hour until it is empty.

For example, for a 1300mAh Lipo, it would take an hour to fully discharge if you draw a constant current of 1.3A from it. If the current draw doubles to 2.6A, the lifespan would be halved (1.3/2.6=0.5). If you draw 39A of continuous current, this pack would only last 2 minutes (1.3/39=1/30 of an hour).

Increasing battery capacity may give you a longer flight time, but it will also increase weight and physical size. There is a trade-off between capacity and weight, which affects the flight time and agility of the aircraft.

A higher capacity could also provide a higher discharge current, as you will see in the next section.

Please note, 1000mAh = 1Ah.

C Rating (Discharge Rate)

Drone Lipo batteries all have a C rating. Knowing the C rating and capacity of a battery, we can theoretically calculate the maximum safe continuous discharge current of a LiPo battery.

Maximum Discharge Current = C-Rating * Capacity

For example a 1300mAh 50C battery has a rated maximum continuous discharge current of 65A.

Some batteries come with two C-ratings: "continuous" and "burst". The Burst rating is only applicable for a short period of time (e.g. 10 seconds).

While the C rating can be a useful tool, it has now become mostly a marketing tool.

If the C rating is too low, the battery will have difficulty delivering current to your motors. You could also damage the battery if the current draw exceeds the safety rating.

When the C-score is higher than the required one, you will not get a significant performance improvement. Instead, the battery would be heavier and you will carry extra weight that reduces flight time.

Connectors

As a general rule, the battery connector should match the one you are using on your helicopter. If you don't have a quad yet, pick one and stick with it.

All Lipo batteries come with 2 sets of wires/connectors: a balance wire and a main wire or discharge wire (except for 1S batteries which only have a main wire). There are different connectors used in LiPo batteries. The main differences are the shape, weight and current rating.

1S Battery Connectors

1S connectors are small and have a very low current rating. They are commonly used in brushed micro quadcopters.

LOSE
Pico's Blade
JST-PH

2S-6S Battery Connectors

You will find many different types of battery connectors in this category, in fact not all of them are listed here. But most of them are not used often, so you do not need to worry about them. For mini quad, the most popular connector is probably XT60.

However, as XT60 is rated at 60A and mini quads run at ever higher current and voltage, we may soon see a change in the popular connector used.

JST		Mainly 2S
XT30		Mainly 2S and 3S
XT60	Similar to the previous one, only bigger	Mainly 3S, 4S
XT90	Similar to the previous one but even bigger
HXT-four millimeters
EC3
EC5	Similar to the previous one but bigger
Deans (T)

Balance Lead

This cable is mainly used for balance charging to ensure all cell voltages are equal. It also allows you to monitor the voltage of each cell.

The number of wires in a balance lead starts at 3 for 2S LiPo, and for every increment in cell count, the number of wires also increases by 1.

Internal Resistance (IR)

Internal resistance exists in every battery cell and the IR may be different in every cell of the same LiPo battery. Higher internal resistance reduces the maximum current that the LiPo pack can produce, which is why as a LiPo battery gets older or overused it will find itself losing punch or power.

IR is not shown on the label, because it can change over time. The internal resistance of Lipo increases with:

• time / age
• freezes (physical damage)
• that downloads
• overheating
• other abusive use

You can measure IR with dedicated instruments, some LiPo chargers also have IR measurement functions.

We covered IR in more detail in the C-Rating article.

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How to choose LiPo battery for quadcopter?

To choose the best Lipo battery for your quad, you first need to know your requirement, preferred number of cells and what would be the maximum discharge current.

Find out how much current your drone can draw

Once you have decided on the size of the motors and propellers, you should be able to find the data online for that requirement. For example, I will use this motor with 5045 x 3 props, at 100% throttle it draws 27.6 amps.

The maximum current draw for a 4 motor quad would be 2767 x 4 = 110.4A at 100% throttle.

How accurate are static thrust tests?

Remember that in real flights, the current draw is usually lower than in "static thrust tests" due to the moving air.

And you notice that the current is significantly different between 90% throttle and 100% throttle, and you should ask yourself how often you should fly at 100% throttle and that interests you.

Personally, I mostly fly at 40%-80% throttle range, even when I punch out at full throttle they won't last more than a few seconds.

Current extraction of other components

There are other parts that also use battery, such as FC, RX, LED, FPV etc. But it is very small compared to the powerful motors, so we usually ignore them from our calculation. Or add 1A to 2A to the current total draft if you want to be a little more precise.

Choosing the Optimal Battery Capacity for Your Drone

Now you need to calculate the battery capacity for your particular quadcopter size and the required C-rating. Here are some general guidelines I personally follow from propeller size:

 6 inch: 1500mah - 2200mah
 5 inch: 1300mah - 1800mah
 4 inch: 850mah - 130mmah 
3 inch: 650mah -1000mah

Flying style affects battery choice

That's right, you need to consider the type of flying you plan to do and whether weight or capacity is more important to you. Hardcore pilots will want the lightest batteries that are just enough to complete the race course. But for "freestylers", weight is not the only priority and larger batteries can be considered for a longer flight time.

How to charge LiPo

Charging type

• Balance Charge - The charger monitors the voltage of each cell and can charge them individually while trying to keep them at the same voltage level. This is the safest and recommended way to charge your LiPo battery.
• Direct Charge (Fast Charge ) - You are charging only through the main cable and the charger is not monitoring the voltage of each cell. This is normally faster, but may cause unbalanced cell voltages and the battery may not be charged to 100%
• Memory Charge - The charger brings each battery cell to the storage voltage, which is 3.80-3.85V
• Discharge - The charger attempts to discharge the Lipo battery (very slowly, even slower than charging)

Why balance the charge?

Each cell in a battery is slightly different, after the battery is discharged, you may find that the voltages of the cells are all different.

If we were to directly charge this unbalanced battery without voltage monitoring each cell, it is likely that some cells might end up below 4.2V (not fully charged), and what would be worse, some might go OVER 4.2V . If you remember, LiPo cells should not go above 4.2V or they will become dangerous. Remember, overcharging = dangerous!

Most decent modern Lipo chargers are programmable and allow for balance charging and should take care of this automatically.

Safety rules

Improper use of LiPo batteries may cause fire. Please take the time to read these safety rules before handling/charging your batteries .

• Get LiPo by their body, not by the wires: the wires could be torn out by the fragile solder joints
• Charge in safe places - It is very important to find a fireproof location to charge your batteries. Using a Lipo-safe bag is a good option, some even build a bunker for it. I personally find using an ammo box to be a cheap but effective solution
• Do not charge the battery immediately after use, wait until it has completely cooled down
• It is advisable to charge the battery at 1C or less
• Never charge the battery unattended - check regularly if the battery is getting hot or starting to swell, if so stop charging immediately
• Never use or charge a damaged battery - do not charge if it is swollen or has other visible signs of damage.
• Make sure the cell count and battery type are set correctly on the charger to match the number of cells in the battery.
• Do not overcharge, although this is normally taken care of by the charger, it would be a good idea to check the cell voltages regularly
• Do not leave the battery under the sun

Parallel charging

Parallel charging may not be the safest way to charge LiPo batteries, but it is probably one of the fastest and most used by RC enthusiasts. It allows you to charge multiple packs at once rather than one at a time. However, you do so at your own risk.

How to Use LiPo Batteries Safely

How to Measure LiPo Battery Voltage

For in-flight voltage monitoring, here are ways to monitor Lipo voltage.

It is important to have a way to check the voltage of each cell in a LiPo to make sure they are roughly the same, such as using a LiPo tester. If a particular cell has a voltage that is much lower or higher than the rest of the cells (or what we call unbalanced cell voltage), it probably indicates a problem with that cell and you should check it carefully and balance the charge before using it.

Working temperature

LiPo batteries for mini quads work between 30 and 60 degrees Celsius.

Cold is a performance killer for Lipo batteries: lower discharge rate and effective capacity. Common descriptions of using LiPo batteries in the cold winter would be "shorter flight times", "lack of punch", and "bad voltage sag".

So make sure to warm up the battery before flying in winter to about 30 degrees to 35 degrees Celsius for optimum performance. (put them in your pocket for example :))

Lipo also doesn't like too much heat. Once they get above 60 degrees, they may start to swell and even catch fire.

When it's time to land

A common question from beginners is, "When should I land?" I would say when the battery voltage reaches 3.5V to 3.6V. For LiPo batteries, you should not run the battery until it is "flat" and you should leave an acceptable level of charge in the pack.

Over-discharging LiPo batteries causes permanent damage to the battery and reduces battery life.

How to store Lipo batteries

If you have decided not to use a LiPo battery for a long period of time (for example more than a week), you should

• Storage charges it at 3.8-3.85V
• Store it in a safe LiPo bag
• Store it at room temperature

When a LiPo cell is at 3.8V-3.85V, it is about 40% to 50% charged, and this is the most stable state for a lipo battery. This is why every time you get a new battery from a store, it is half charged.

It is not only dangerous to leave a fully charged LiPo for a long time, but it may also reduce its performance over time. If you fly every few days, then this is less of a problem for you.

Safe LiPo Bags

LiPo bags are the must have investment for your LiPo batteries. They are used to charge and store your batteries. LiPo bags are designed to contain the flame when a battery fire occurs.

CONCLUSIONS

Be sure to check that the battery is used safely and last a long time.