Proper charging protocols are the beginning of excellent FPV battery maintenance. When charging your batteries you want to take a few things into consideration. First, would be the capacity of your battery. Capacity is defined by how much charge your battery can both store, and deliver, and is rated in amp hours, or Ah. Because of the size of our batteries, that is often reduced to milliamp hours, or mAh. One of the most common capacities in use for multirotors would be the 1300 mAh battery, and as such will be the one that we will be using for our example.
On a safety note, never leave your charging batteries unattended. The hobby is rife with examples of LiPo fires taking out a pilots gear, garage, or entire home. Even with someone paying attention, these things can happen, but by being around your batteries when charging, you can react to a situation much quicker. Proper FPV battery maintenance always starts with good safety practices.
Parallel charging can be a way to get several batteries charging at once, but use with caution. The way parallel charging works is by using a charging board specially designed to accomplish this task. When several batteries are hooked up to the board, the charger sees them as one large battery. In order to charge these batteries at the same rate as you would a single battery, you need to do a little more math. In our example, we are going to use the 1300 mAh battery again, and we are going to charge six of them together using a parallel board. Using this equation, we can determine what 1C is; cA=6(1300 mAh / 1000). From this equation, we get 7.8 amps. Now if we wanted to charge at 2C, it would look like this 2(cA) = 6(1300 mAh / 1000), resulting in 15.6 amps.
There are three things to consider about parallel charging when considering proper FPV battery maintenance. Firstly, never charge batteries that have a different number of cells together. For example, do not charge 3S batteries with 4S batteries. Doing so will damage your batteries, might damage your charger, and may start a LiPo fire, which we should avoid.
Secondly, batteries that are to charge together need to have very similar voltages. Optimally, they need to be within .10 volts from each other. If they are not, you may need to “bump” charge them to get them within that range. Not heeding this advice can lead to batteries with a higher charge dumping that charge into the lower charged batteries and a very fast rate, damaging both.
Lastly, and most important, internal resistance rears its ugly head here. Think of internal resistance as a virus that infects your batteries. That virus can “transmit” to your other batteries through the parallel charging process. So if you have a bad battery, and you charge it together with other batteries, you can corrupt all the other batteries.
I’m not going to tell you not to parallel charge, but ultimately if you want to make sure you don’t corrupt your batteries, or don’t want to have worry about matching voltages, you may want to look into a multiport charger. It’s truly the safest option out there.
Alright, so we have our batteries charged, now we get to go out and rip with abandon right? Not so fast there, Sparky! Discharging your batteries through the use of them on your model is where the most damage to your battery can, and will, occur, and is the place where we absolutely must practice proper FPV battery maintenance.
First off, never discharge your batteries completely. This will cause your batteries to heat up to levels that are out of specifications for the battery. Remember, excessive heat builds up internal resistance. The maximum that a battery should discharge to is 80% of the total capacity. So in the case of our 1300 mAh battery, that equates to 1040 mAh drawn out. Additionally, never discharge any individual cell below 3.0 volts. In a 4S battery, using this standard, overall voltage should not come to a resting state below 12 volts (3 volts X 4 cells). Personally, I don’t draw down my 4S batteries below 13.8 volts.
Another cause of battery damage is drawing the battery down too quickly with long duration high throttle. Doing so will over tax the battery, again leading to high heat generation. Keep your boosts of throttle relatively short, optimally less than ten seconds in duration.
The last thing we are going to cover for proper FPV battery maintenance is the correct storage of your batteries. When you get home from the field, one of the first things you should do is to set all your batteries to storage charge. This will put them at the nominal charge for being put away on the shelf, and ensure that they are ready for the next flight session. This also puts the battery in a stable state, in which the likelihood for damage and build-up of internal resistance is much less.
If you have fully charged batteries that you aren’t going to use relatively quickly, such as the next day or so, then go ahead and discharge those to storage charge as well. Leaving a fully charged battery to sit for longer periods of time will cause some damage. Nominally, the voltage for should be around 3.8 volts per cell to be at storage.
This also gives you a chance to inspect each of your batteries for any damage after your flight session. You want to look for issues such as cut cables, damaged connectors, holes and punctures, and dents or bends in the individual cells. Any kind of damage needs to be assessed for both safety and viability of the battery, and a decision needs to be made if the battery can be still be put back into service after repairs.
Batteries are expensive, and without them, you aren’t going to be flying much. Taking the time and effort into proper FPV battery maintenance will protect that investment, and keep you in the air. It also means that you won’t need to replace bad batteries as often, saving you money for all the other things you want, like new models! These practices will also keep you, your family, and your things safe. Remember, LiPo’s can be volatile when not properly cared for!