Batteries

The heart of your FPV drone is its power source, and when it comes to drone power, LiPo (Lithium Polymer) batteries reign supreme. These high-performance batteries pack a lot of power, but they require proper care. Misuse can turn them into bombs, literally!

This guide will help you understand the basics of FPV batteries. The most common FPV batteries are Lithium polymer batteries, more commonly known as LiPo, which have incredible power to weight ratio! Let´s get to know these batteries.

Battery Voltage

A single LiPo cell holds a nominal voltage of 3.7V. This is the voltage number LiPo battery use on their labels. However, the safe operating voltage range is between 3.0V to 4.2V. Overcharging above 4.2V or discharging below 3V could cause irreversible performance loss or even a LiPo fire.

It´s generally recommend to stop discharging a battery when it reaches 3.5V per cell to prolong battery lifespan. This is known as the cut-off voltage.

Cell Count

A LiPo battery can have multiple LiPo cells, common LiPo batteries for 5-inch FPV drones are 4-cell (or 4S) and 6-cell (or 6S). When higher voltage is required, LiPo cells can be connected in series to form a bigger, higher voltage battery.

Battery voltage has a direct effect on how fast the motors can spin, therefore you could use a higher cell-count battery to increase your drone’s power (assuming the electronics in the drone support the higher voltage). However, adding more cells to a battery also means it’s heavier.

In FPV, we don’t normally refer to the total battery voltage because it’s mouthful, we just call them by the number of cells, or how many “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

For example, we call a 14.8V battery a “4-cell” or just “4S” battery.

Capacity

The capacity of a LiPo battery is measured in mAh (milli-amp hour). This unit signifies how much current you can continuously draw from the battery for an hour until it’s empty. A higher capacity might give you a longer flight time, but it also adds to the weight and size of the battery. Striking a balance between capacity and weight is crucial for optimal efficiency.

C Rating

The ‘C’ in ‘C rating’ stands for capacity. The C rating of a LiPo battery indicates the maximum safe continuous discharge rate of a battery. If a battery has a capacity of 1000mAh and a C rating of 20C, it means it can be discharged at 20 amps continuously without causing damage to the battery or reducing its lifespan. Higher C ratings mean the battery can safely discharge at higher rates, providing more power for demanding maneuvers.

Internal Resistance

All electrical components, including batteries, have resistance. In a battery, this resistance is internal and can be used to measure its performance. Lower internal resistance means more effective power delivery. Over time, poor practices like over-discharging, over-charging, and overheating can increase internal resistance, indicating it may be time to retire the battery.

Discharge Connector

LiPo batteries feature a discharge connector (main lead) and a balance connector (balance lead). The discharge lead, consisting of thick red and black wires, powers the FPV drone. Commonly used connectors include XT60 for 5″ drones or larger and XT30 for smaller drones.

Balance Connector

The balance lead allows the charger to monitor and balance cell voltages during charging. Always connect this lead before charging! The number of wires depends on the battery’s cell count.

How to use LiPo Batteries Safely

Don’t leave them fully charged or empty for long

It is best to use any fully charged LiPo as soon as you can, and return it to storage voltage when it’s done.

That is because when a battery is not at its storage voltage, it’s constantly degrading over time faster. In general it’s ok to leave batteries fully charged or discharged for a few days.

But if you don’t plan to fly for longer than a couple of weeks, it’s probably best to put your batteries on storage charge.

Working temperature

FPV drone LiPo batteries has the best performance between 30°C to 60°C.

Cold weather is a performance killer to LiPo batteries, you have worse voltage sag and flight time. Try to keep your batteries warm before a flight

LiPo doesn’t like it too hot either, when it gets too hot they could start to swell and even catch fire. So make sure you don’t leave them under the sun in the summer!

When to land

You should land when your battery voltage reaches 3.5V to 3.6V.

You could keep flying until voltage is even lower, but it puts extra strain on the battery and might shorten lifespan faster. All cells are different in a battery, when you give the drone a burst of throttle the battery will sag and some cells might sag more than others and go below the safe limit and risk causing damage to those cells. Landing a bit early at 3.5V reduces the chance of that from happening.

Another reason is that the voltage drops a lot faster below 3.5V, if you keep flying you can risk over-discharging your battery before you can land safely. Over-discharging can cause permanent damage to the battery, and shorten battery life.

Credit to oscarliang

What to do when a battery is on fire?

  • Don’t panic, unplug all connection first if possible
  • Use fire extinguisher
  • If that’s not an option, sand is also an effective way to put out LiPo fire, cover the burning LiPo with sand
  • do not breath in the smoke, just wait until the fire goes out and the battery is cool
  • Do NOT use water ever

Li-ion batteries

While LiPo batteries are widely used in the FPV world for their high discharge rates and power output, Lithium-ion (Li-ion) batteries have recently gained attention for certain FPV applications. These batteries are different from LiPo batteries in a few key ways.

Li-ion batteries are known for their higher energy density, which means they can store more energy than LiPo batteries of the same weight. This leads to significantly longer flight times, making Li-ion batteries a great choice for FPV pilots who prioritize flight duration over raw power output, such as in long-range cruising or exploration flights.

However, it’s important to note that Li-ion batteries generally have lower discharge rates compared to LiPo batteries. This means they might not be able to deliver the intense bursts of power required for high-speed racing or advanced acrobatics.

Li-ion batteries also require special care, just like LiPo batteries, when charging and discharging to ensure their longevity and safety. Overcharging or discharging them too much can lead to irreversible damage.

Understanding FPV batteries intricacies and following safe practices can significantly improve your FPV drone’s performance and lifespan while ensuring your safety 

Check out our next article on chargers and how to charge the batteries here

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