The nominal voltage of a LiPo cell is usually 3.7 V. if you get to see, for instance, a 7.4 V Lipo cell, this means that two cells are connected in series (which means that the voltage is added together). For this reason, you may sometimes hear people talk about a "2S" battery; what that means is that two cells are in series. A pack of 2 cells (2S) is 7.4 V; consequently, a package of 3 cells (3S) is 11.1 V, and so on.
At the start of the use of LiPo batteries, you may have seen a battery called "2S2P".
What that meant is that there were four cells in that battery; two cells connected in series, and the other two connected in parallel with the first two batteries (by parallel, that is to say, the capacity gets added together). This terminology is no longer widely used these days. Thanks to modern technology, individual cells can now store much more energy than a few years ago. However, it is still essential to know the above or older terms because it can be helpful if you come across something done a few years ago.
The voltage of your battery pack inevitably determines the speed of movement of the application of the battery, be it a vehicle or whatever you are using it for. Voltage has a direct effect on the speed (RPM) of the electric motor (remember, brushless motors have a nominal power rated in kV, and that means "RPM per volt"). Consequently, if you have a brushless motor that is rated 3,500 kV, such a motor will rotate at 3,500 rpm for each voltage applied. With a LiPo 2S battery, this motor is going to spin at about 25,900 rpm. In a 3S, it rotates at 38,850 RPM. The more the voltage on your battery, the faster you will go.
What is the lowest voltage for a Lipo battery?
If you allow your battery drop below 3.7 V per cell, you will begin to notice a sharp drop in performance, and the voltage of the cell will form the habit of dropping quickly under load.
Most battery experts would say 3.0V is the accepted lowest voltage you can allow your Lipo battery to reach and warns that going below that will trigger some damages.
However, do not confuse the minimum voltage with minimum storage voltage. LiPo batteries must be kept at about 60% of storage voltage when the batteries are not in use. If a proper charger is used, the final voltage must have been set. As we have already stated above, you do not want to use your Lipo batteries beyond 3.0v because that will bring about damages to the cells. This is why it is so important to balance LiPo batteries. This is because one of the cells could be 3.2 V, and the other maybe, 2.8 V, and you may not know until one of the cells broke utterly.
It is preferable to use a slightly higher cutoff. So, in other to maintain your battery and not allow it to drop below the limit, you may set a reminder or your alarm to remind you when the battery voltage reaches 3.2-3.4 V range. This will allow you to enjoy an excellent pack-life with no puffing.
If you leave your battery for a while, the voltage will bounce back up or recover just a bit. It may even raise to about 3.7V per cell -this is known as the resting value. And there is Little power/run time below the resting voltage.
Below is a typical resting voltage versus capacity table for Lipo batteries that are discharged to 3V per cell cutoff (under load):
4.20 V = 100%
4.03 v = 76%
3.86 v = 52%
3.83 v = 42%
3.79 v = 30%
3.70 v = 11%
3.6? V = 0%
For the best Lipo battery life, it is recommended that you limit the discharge of your battery to 80% discharged (that is, 20% capacity must be left in the battery). This will ensure you enjoy the best battery life.
How do you care for Lipo battery voltage?
For battery experts, they know every battery, including LiPo batteries, is quite dangerous, but many people who are not too into batteries don't know this.
It has been known for years that lithium polymer batteries (LiPos) are dangerous and, in fact, unpredictable. Dropping, bruises, or denting can shorten battery life and may bring about an internal short circuit, which is a recipe for fire. There are countless guidelines for storage, recharging, and transporting your batteries.
1. Attend to your batteries
Of course, the very first tip in the care of LiPo batteries is that the batteries are never left unattended during their charging or discharging time.
2. Don't ignore your manual
Then you must read the manual attached to the battery when you bought it.
Check the battery voltage before each charge to make sure it matches at least the minimum safe start voltage -or is above it. If the starting voltage is lower than the recommended values, then the Lipo battery has been excessively or over-discharged, or there has been a fault, and the battery should NOT be charged.
3. Check for damages
Always ensure you check the battery before you go ahead to charge it. Check that the packaging of the battery, cables, and connectors are free from faults, which could cause a short circuit and possible battery failure.
4. Properly charge the battery
Use only a charger meant for lithium-polymer or lithium-ion batteries. To ensure the voltage is maintained, do not discharge the batteries at an amperage rate higher than what is indicated on the label.
To keep your battery voltage, never allow the battery temperature to exceed 140°F when the battery is being discharged.
It is pertinent to note that batteries may accidentally leak within an hour of being discharged, and this reaction with air can ignite the chemicals. So, keep your batteries in a safe place away from flammable materials and monitor them for one hour after their discharge.