Best Lipo Battery : Lithium Polymer Battery Buying Guide and Reviews

Read this before you buy lipo batteries ...

In the recent years, the LiPo batteries have come to dominate the hobby market and are now widely used in multirotors, RC planes, boats, vehicles, helis and so much more. LiPo batteries need to be taken good care of - else they may be dangerous. These batteries need to be used with care – make sure you follow all of the recommended safety measures while storing, charging and using them.

On the other hand, these batteries are can supply between three and five times the energy produced by other types of batteries such as NiMH and NiCd rechargeable batteries.

Lithium Polymer batteries have a strong energy density and can handle more energy compared to batteries of comparable weight.

You can say lipo batteries are possibly the number one reason why most RC vehicles – including drones – are now electrically powered. You do not need to use gas powered engines anymore. Lipo battery powered drones are so much more quiet and clean – and a lot safer as well. Had it not been for lipo batteries, quadcopters would most possibly not have become as popular as they are now.

Here are some of the main advantages of lipo batteries …

  • These batteries are light weight and are available in a wide range of shapes and sizes.
  • Lipo batteries have a much greater energy density compared to alternatives like NiCd and NiMH batteries.
  • Lithium Polymer batteries with very high charge and discharge rates are now available. So you can charge them pretty fast and use them to operate very power hungry electrical motors.

What to look for when purchasing LiPo batteries

'C' Rating

The discharge rate of your lipo battery – indicated by C – is the rate at which you can draw current from your battery.

Batteries with a high discharge rating can supply more current in less time; On the other hand, if the discharge rate is low you will not be able to draw a lot of current fast from the battery.

It’s important that you choose a battery with a discharge rate that’s higher than what your quadcopter needs. If your quadcopter is to perform well, your battery should be able to easily supply the current the drone needs. Else, your drone will not perform well and you might end up causing damage to the battery.

You could say the discharge rate measures how fast energy can be extracted from the battery. If the motors take in more energy than what the battery can produce, then the battery can easily get damaged, and this could mean your drone might crash. The motors consume the most power. Power consumed by ESCs and transmitter is not very high. 

Every battery needs to have two ‘C’ ratings mentioned – maximum continuous current and burst current. Many battery packs do not always carry the burst current rating.

Maximum Continuous Current

C means Capacity rating. This is the safest continuous rate of discharge of a pack. The continuous current (mAh) that can safely be drawn from a battery is obtained by multiplying the batter’s C rating and the cell capacity.

For instance, if your battery’s C rating is 15C and the cell capacity is 1000 mAh, then the continuous current the battery can supply is given by

Continuous current = 15 x 1000 mAh = 15000 mAh

Or a continuous discharge rate of 15 Ah.

Which essentially means the battery can supply a current of 15 amperes continuously for about an hour.

Burst Current

For very short periods of time, say for about 15 to 30 seconds, batteries can supply a current much greater than the maximum continuous current they are able to supply.

This is the burst C rating of the battery.

Calculating Flying Time

You can use the battery pack’s capacity to calculate how long your drone will be able to fly.

Let’s say the capacity of the lipo pack you are using is 2000 mAh; And the C rating is 20C;

And let’s suppose your drone requires a current of 20A

Flying time = (2000 mAh/1000)/20 A x 60 = 6 minutes

So if your drone will be drawing a current of 20A from a 2000mAh battery pack, it should fly for around 6 minutes.

This is just an estimate. Actual flying time depends on factors like wind resistance, load, ambient temperature and your flying style.

Charging Lipo Batteries

Ideally, you should be charging most lithium polymer batteries at 1C charge rate. Whatever the ‘C’ rating for the battery is, you would want to be charging the battery at that rate : 1 x Capacity.

Suppose you have a 2200 mAh battery, you would want to charge it at 1x 2200 mAh = 2200 mA

Or 2200/1000 = 2.2 Ah

On your battery charger, you would want to specify 2.2 A and charge the battery.

You will always want to refer to the battery manufacturer’s manual before you decide to charge the batteries at a higher charge rate.

These days, you will find batteries with 2C and 5C charge rates. This means you can charge you battery at least three times its capacity.

For example, 2000mAh, 2C pack can be charged at (2000 mAh x 2)/1000 = 4 Ah

The best thing about this new technology is that it lets you charge your LiPo battery in only fifteen minutes. However, for safety purposes make sure you don’t charge the batteries at higher charge rates – unless the manufacturer says this can be done.

If you are not in a hurry, you would want to charge the battery at around 1C so as to maximize the life of your LiPo battery. While charging at these rates, it is paramount that you monitor the battery constantly, to prevent any damage from taking place.

However, you need to be very careful. Well, it may sound great to charge the battery for less than ten minutes, but then again, you should try as much as possible to prolong the battery lifespan. Avoiding using the maximum charge rate, but instead use 1C.

In addition, you will want to ensure you always use the charger your battery’s manufacturer recommends. This is very important if you are charging several batteries simultaneously.

It might be tempting to charge your batteries at a high rate. Charging your battery at 10C will be nearly 10 times as fast as charging it at 1C. But you would want to know what you are doing before you do something like this.

If the manufacturer recommends the battery should be charged at or lower than 2C and you charge it at 10C, the battery will most likely blow up. That could be a very dangerous thing. Lithium Polymer batteries need to be handled with a lot of care – and over charging a battery is something you would never want to do.

It’s always a good idea to charge your lipo batteries outside your home.

You would also want to ensure that you never short circuit the battery. This can kill the battery in less than a second. And if you suspect a battery is dead, check the voltage. If the voltage is less than 3.0V, it’s most likely damaged and you should never try to charge it again.

If the voltage falls below 3.0V, dispose the battery. But don’t throw it in a trash can – that’s a very irresponsible and dangerous thing to do. A physically damaged LiPo battery can explode and endanger other people.

Before you dispose a lipo battery, you should discharge it completely to 0 Volt. Never throw your batteries in the garbage before they are completely discharged.

Refer your manufacturer’s manual for instructions on how to discharge and dispose the batteries.

Battery Balancing

You want all of the batteries in your lipo battery pack to have the same voltage.

The individual batteries within a battery pack may have slightly different capacities and contain different levels of charge. So the battery with the least amount of charge can get discharged before the rest of the batteries in the pack.

And while charging, the battery with the least capacity might get overcharged before the battery with the highest capacity can get fully charged – and this scenario can be dangerous.

Battery balancing is a technique that’s employed to redistribute the charge so that all of the batteries in a pack are evenly matched.

Battery balancing does not happen automatically whenever you charge your battery pack. Your battery pack needs to be connected to the balanced port of the charger through the individual JST plug. Or else you will not be balance charging your pack.

The Number of Cells

This is also one of the most crucial factors to consider when looking for a LiPo battery. Batteries are made from rectangular cells which are then interconnected to form the battery. A normal battery cell is capable of handling about 3.7 volts. When you link some of these battery cells together, the voltage increases to about 7.2 volts, if you are using two battery cells and 11.1 volts for three cells. If you connect several batteries in a parallel manner, the capacity increases.

Most of the time, you will see a number such as 3S2P. This just means that the battery features three cells connected in series and two others connected in a parallel manner to make a total of 6 cells inside the battery.

Therefore, the number of cells in a LiPo battery is what determines the voltage the battery. A battery with a higher voltage can offer more energy to power even the largest motors. However, do not confuse power with durability. Having a battery with more power doesn’t mean it can last for a long time. The battery capacity is what determines the durability of the pack.

Voltages

Each cell inside the battery features a nominal voltage of 3.7 volts. In contrast, NiMH and NiCd cells have a nominal voltage of 1.2V.

This means battery packs containing LiPo batteries need to have fewer cells per pack. And very small, nano and micro quadcopters can fly having only a single LiPo cell.

The larger drones may need anywhere from 6 to 12 cells connected in series to operate.

Two battery packs can be connected either in series or in parallel.

Depending on what you want – more power or more flying time, you could choose to connect battery packs either in parallel or in series.

Batteries in parallel

If you want higher currents, you could connect battery packs in parallel. The diagram below shows two lipo batteries connected in parallel.

Both the battery packs have the same configuration : 3S, 2000mAh, 10C. The output voltage and current of each of the packs are 12.4V and 20A.

When the packs are connected in parallel, the combined output is 12.4V and 40A.

So if you need to draw more current, connecting the packs in parallel can help you achieve it.

You would want to note that you would not want to connect batteries of different voltages and capacities in parallel. Supposing you do that, the battery with the higher voltage will discharge into the other one with the lower voltage.

If that happens, the resulting high current – which will flow very quickly - might damage one of the batteries. And since we are talking about Lipo batteries, one of the batteries might get damaged permanently.

Warning - Do not ever charge your batteries in parallel !!!

You would also want to note that you would never, ever want to charge your lipo batteries in parallel. No battery charger will be able to monitor the voltages of the individual cells in the pack. And that’s what makes parallel charging very dangerous.

Parallel charging should not be done – not even by experts. There are so many parameters you would need to monitor while charging lipo batteries in parallel – and it well beyond any individual. Only manufacturer who are able to carefully control all parameters in their plants can charge batteries in parallel.

Don’t use parallel charging chords. Don’t charge lipo batteries in parallel.

Lipo batteries must always be charged in series and never in parallel – no matter what.

Batteries in series

The following diagram shows two lipo packs in series.

The voltage of the combined packs increases to 24.8V, while the current stays at 20A.

Internal Resistance

This is a number that is hardly ever mentioned on any battery pack, but that doesn’t mean it isn’t important.

In fact, the internal resistance of your battery – measured in milliohms – has a huge impact on the output voltage and hence on the performance of your drone. This number is not a constant and increases with usage. It can also vary widely across different batteries.

For new lipo batteries, this can be one measure of the quality of the battery. Lower the internal resistance, the better the battery’s quality tends to be.

The voltage tends to go down if you continue to use the battery for some time. This happens because of the increase in the internal resistance of the individual batteries.

As the internal resistance of the battery increases – and it does increase over time – the output voltage falls. The performance of the battery likewise deteriorates. Measuring the internal resistance of a battery usually requires expensive devices. Some of the high end battery chargers come with software to measure the internal resistance of lipo batteries though. Investing in such a charger would be a good thing to do.

New lipo battery packs usually have an internal resistance of less than 5 milliohm. And battery packs that need to be retired typically have an internal resistance of more than 20 milliohm.

After a while, the battery will not be able to hold its charge for more than a few minutes. And you will need to retire the battery.

However, you need to make sure that the voltage doesn’t fall below the 3.0 volts.

On the same note, you must make sure the optimum voltage for the battery cells is 4.2 volts. If the voltage increases above this point, then the chemicals inside the battery cells will become unstable and may cause a fire. This is the reason why LiPo battery chargers are made to make sure that the battery cells charge only up to 4.2 volts. Most of the devices come with a cut-off voltage feature which immediately switches off the motor when the battery voltage becomes too low so as to prevent discharging.

Are used Lithium Polymer batteries worth purchasing?

The majority of used LiPo batteries have not been used at the top current drain. However, this is not a big issue because the user is unlikely to have over drained it. However, if the battery is over drained, it might explode as the pockets of the battery expand due to excess load. Therefore, you need to check on the images keenly and get extra ones so that you make sure no expansions have occurred.

In addition, another crucial factor is the integrity of the LiPo battery, more so on the outer part of the battery (the casing).

It’s also very important that the battery has not suffered any physical damage. You would never want to use a battery that’s been damaged physically.

Things to note

You should never buy a LiPo battery that has splits, slight cracks or any other signs of damage. This is a factor that needs not to be re-emphasized. If you happen to purchase a ruptured battery with a casing that is damaged, then it is more likely to cause more harm than good, especially if it is under extreme load. Remember, Lithium Polymer batteries are made with a lot of dangerous chemicals that can harm you and the environment around you.

Precautions to take when charging your LiPo battery

  • The most important thing is to ensure the charger settings – for voltage and current – are correct and appropriate for the batteries being charged.
  • Always be around whenever you are charging your LiPo batteries, you should never leave the batteries to charge while you are away. It can be very dangerous.
  • Also, you would want to charge – and store – your lipo batteries inside a lipo sack - or a lipo bag. A lipo sack is fire- proof, but that still doesn’t mean you can be away from your batteries while they are being charged.
  • Investing in a lipo battery tester and a battery monitor would be a very good idea.  Lipo batteries tend to be unstable, and you will want to ensure the voltage levels are at acceptable levels when you want to use them. 
  • It might be a good idea to use the same type of lipo battery connector on all of the batteries you use. 
  • And you would want to ensure no flammable materials are close to the batteries while they are getting charged. Ideally, you would want to charge your batteries outside your home – maybe on a concrete patio.
  • If you notice the battery becoming puffy or if you see any smoke, you should be in a position to handle the problem. If you stay away for a few minutes, it can create a huge disaster. Having a dry fire extinguisher or a bucket full of sand close by is a good idea.
  • You would want to purchase a Class D fire extinguisher if you do not have one. Keep it near where the battery is charging or in a storage area that is easily accessible. Make sure the storage or the charging area is as clean and empty as possible. Get rid of any materials that can easily catch fire. These materials include carpets, wooden tables, and even gasoline containers.
  • You would want to keep batteries away from children or pets at all times – even while the batteries are not being charged. You would never want a child to lay their hands on a lipo battery.
  • Make sure that the LiPo battery charger or discharger has proper balance, especially when charging your batteries. Also, it is imperative that the battery cells have the same voltage all the time. If there are discrepancies in the cells voltage, then the battery may become unstable, and this is not a good thing. But if you are using one cell, then there is no cause for alarm.
  • There are many LiPo chargers with digital displays on the market, and those are the ones you need to use. Do not use the NiMh and NiCd battery chargers. Another important thing you should check out when purchasing new LiPo batteries is the second lead. The latest versions come with a second lead material which helps to balance charging because each cell inside the battery is usually charged independently.
  • If you have never used a LiPo battery before, then you should buy a Balance LiPo Charger. But if you have been using LiPo batteries for some time now, you may want to upgrade your charger as well.

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