I purposely dated this post as I am sure as time continues on, I will have more lessons learned to add on as I continue to fly and learn what works and what doesn't.
My situation is perhaps unique as I am retired, absolutely love to fly, my flying field is less than 10 minutes drive from my house, I am NAMC's main test pilot and also do a lot of field testing of different components for our recommended parts list, so I accumulate a lot of flights on a regular basis. I can also fly almost all year round, October and March at times tend to be a bit nasty with winter and spring storms, but other than that I can fly the year round. As such, I average about 120 flights per month, so my batteries get a lot of use. I admit that some of the techniques I use might "fly in the face" of conventional thinking about Lipos, I don't know, but I know these have worked for me safely and efficiently over a long period of time and a lot of use from my batteries, so I won't argue with success.
All the batteries I use have been purchased from Hobby King, buying from Canadian online vendors is cost prohibitive, even after paying Fed Ex shipping, duty and taxes, the batteries I use from Hobby King end up cheaper than similar batteries purchased in Canada. Most US distributors won't even ship to Canada and again if they did, they would be more expensive. I try to keep an eye out for good sales with Hobby King and in the meantime just take good care of my batteries :)
Of all the batteries I have used, the most durable, reliable and best performing 2200 3S battery (the size of battery I fly with about 99.9% of the time) for every power setup I have ever run is the Zippy Flightmax 2200 3S 40C. As mentioned, I have some of these batteries that I have been running for three years that still run well, some are a bit tired, but still give me the power I need to have lots of fun. For the power systems I run now since I don't use the NTM 2700 set up any longer, the C rating of these batteries is probably a bit of overkill, but I will continue to purchase and use them as they have worked so well for me over time and as I will discuss a little later I think I wouldn't go any lower on the C rating even with the lighter power systems I run now.
I purchased these Zippy batteries in essentially 3 big lots and run 26 of them in total now, having had to retire a few already. Since I fly so much, each battery gets probably one if not two cycles per week, so they get charged and discharged on a pretty regular basis. From left to right, here are examples from the three batches I bought. Unfortunately, I did not write a date on the one on the left, but I looked back and they were purchased in late 2013. The battery in the middle started use in August 2014, so just over two years ago and the one on the right December 2014, so almost two years ago.
I charge my batteries almost exclusively on balance setting on my charger. I can count on both hands how many times I might have had to fast charge a battery at the field in the last four years, so they always get balanced charged at the field and at home. I know there are many schools of thought on what amp or C rating to charge on balance setting, I used to charge my 2200 batteries at 1.1A, but that took a very long time, so for the past couple years, I charge them on 2.2A using these inexpensive chargers that are available all over the internet. I very rarely purposely put my batteries on storage charge unless they have been charged and I know due to weather or other commitments I won't fly for 4 days or more. Any less than that, if I have charged them and they sit for a couple of days before being used, I don't worry about it too much.
I have found over time that Lipo batteries seem happiest in a temperature range of between 5-25C (41-77 F). I certainly use my batteries outside that range, but take some precautions when doing so.
First let me explain what I have seen. Sometimes when pushing a battery hard outside the temperature zone I mention, I notice that the battery either discharges more quickly or cells will discharge more unevenly than normal, both situations which can lead to damaging the battery if it is pushed too far or too close to the limit too often.
When it is cold, I try to keep my batteries warm before using them, a couple in each pants pocket helps them out and if my session is going to be a long one, fortunately there is wood stove in our field clubhouse, so I get that going and leave the batteries inside to stay warm and then refill my pockets as I use up the batteries.
In hotter weather, I always keep my batteries in the shade to keep them as cool as possible.
Outside the temperature range above, I try to discipline myself to reduce the number of wide open throttle runs or other type flying that puts big strain on the battery. Or if I need to evaluate something and need to keep flying as normal, I will reduce the flight endurance by 30 seconds and this seems to keep my batteries healthy.
How low do I run my batteries?
As you might know, the default low voltage cutoff (LVC) on most ESCs is 3.3V per cell. When you hit this point, your available motor power drops by about 50%, your servos will still work, but you have very little motor power. I admit to running my batteries down this low when I started and I still see videos of guys doing it and guys doing it at my field. Planes get lost when this happens in my experience as you don't have enough power to get to the runway, avoid the ground, trees, etc, so in my opinion and from hard earned experience it is never a good idea to fly to LVC.
Perhaps this is where confusing information plays a part. I have read folks saying "never run your Lipos below 80%". So if you look at a fully charged cell being theoretically 4.2 volts, take 80% of that, you get 3.36 volts and being humans we figure it is OK to go that low and many folks still do and it works out for them. In my experience however, it shortens the life of the battery significantly as you are constantly pushing the battery to this limit.
Fortunately, not long into my RC journey, I read another theory that said to not run the batteries lower than 3.7V per cell which makes sense as you often read that 3S batteries are 11.1V (even though they are 12.6V when fully charged). Again, another mystery I am still trying to figure out :/ I find this allows me a good 5 minute flight with lots of "thrash and dash" (aerobatics and high speed runs/vertical climbout) and I still land with 3.7+V in each cell of my battery, tested as soon as possible after landing before the battery starts to recover. In actual fact I set my transmitter timer for 5 minutes and it starts to give me the countdown at about 4:30. I am probably touching down at about the 4:45 mark on most of my flights, but I have the confidence that if I had to go around after a bad first approach, I will still have plenty of power to attempt a second and maybe even third attempt at landing
Keeping this 3.7 V number in mind, I can monitor my batteries and if I start to consistently see one or more cells below this number, then perhaps it is time to change how I use that battery to further extend it's life.
What do I do as my batteries get old or tired?
When a battery of mine starts to get a bit "tired" or the voltages are not what they once were as described below, I continue using them, but consciously reduce their work load in an effort to extend their life. I will do this primarily by restricting their use to planes with a "mild" motor setup from our recommended parts list. These motors routinely draw in the neighborhood of 26 amps, the other motors I run from the "medium" and "hot" categories draw 30+ amps. I know this doesn't seem like much, but it does make a difference to the battery in my experience.
Some "deeper" thoughts :)
I may have touched on the fact that one of the reasons I selected the Zippy Flightmax 2200 3S 40C battery is that it was versatile for all the power setups I ran, including the big "V8" park jet motor, the Hobby King NTM 2836 2700 motor which unfortunately is no longer available. This motor on 3S draws in the neighborhood of 55 amps with a 6x4 APC prop which is what I used exclusively on this motor, so knowing that fully charged, the Zippy battery should deliver 88A, I knew I was good and for the most part this battery handled that big motor really well, but was still hard on batteries.
So, I suppose as much as I hate to admit it, I kind of outgrew the need to have such blinding speed in my planes, all part of getting old which we all hate to admit I guess. And more practically, I did notice that this motor setup was much harder on my batteries, even though my thinking based on what I knew at the time was correct.
Now perhaps my thinking is off here a bit, but I hope that it makes sense. I know that normally the higher the C rating, the heavier the battery, so while in theory I could probably fly my "mild", "medium" and "hot" set up planes with lower C rated/lighter batteries, but a bit more thinking makes me realize the batteries I am using are still a very good if not the best option for their long term health and durability.
As I mentioned in the first post, if the formula for amp delivery capability of the battery is amps multiplied by C rating, then the fully charged Zippy battery is theoretically capable of delivering 88A. We probably all notice when we punch the throttle early in a flight, we get a little better "pop" than in later stages of the flight. So as I was charging a battery several months ago, it hit me. On average, when running my batteries down to 3.7V per cell as mentioned above, it takes about 1350 Mah or 1.35 amps to fully restore the battery to a full charge. So it made me think that the battery's delivery capability in amps diminished as the "tank" was emptied. So if theoretically a 2200 Mah battery was taken down to 850 Mah, if I run the formula again, 0.85 times 40, the battery is delivering only 30A maximum at the end of the flight. The Zippy battery in fact has a burst capability (probably 10 sec or less) of 50C, so 0.85 times 50 delivers 42.5.
This 30/42.5A is still quite sufficient for the motors we have now on our recommended parts list as even the "hot" combo pulls a maximum of 37A. However, if I think back to the NTM combo needing 55A, I was pushing these batteries awfully hard in latter stages of the flight as I tended to have a "heavy" left thumb when I flew those motors. Again, I might be totally off base with this notion, but I think it makes sense and is a rule that I will continue to apply as I select batteries for long life with my selected power systems.
My 75% rule
This rule again is nothing scientific really, just something I came up with as a personal guideline for selecting ESCs and batteries that will support motor/prop combos that I want to test or like to fly with. You can find lots of test data in the ESCs, Motors, and Props areas of this blog. Sometimes this rule also doesn't apply as the quality control of certain components or what the manufacturer claims they are capable of doing is not exactly correct. Unfortunately, sometimes only personal testing and experience will tell you what works best with your set up, but the batteries and ESCs I like to use have worked very reliably over a long period of time and I have no problem recommending them to folks.
When I look at selecting an ESC or battery, I find the burst rating and take 75% of that. If my motor/prop combo are pulling that number or slightly less, then I am normally good to go regardless of the time of year to ensure good operation and minimal heat build up. Again, sometimes it will depend on the age and quality of the battery or the quality of the ESC. For our line up of motors on the recommended parts list, I have found that the Turnigy Plush 40A ESC is the most reliable, best performing and durable ESC I have ever used. If I apply the 75% rule to this ESC which has a 55A burst rating, I get 41.25A which is well above any of the motor combos I run on 3S.
If I apply this 75% rule to the Zippy Flightmax battery which has a burst rating of 50C, I get 37.5 which is still sufficient to accommodate any of the motors I use now. I know scientifically this might not make sense, but it seems to always give me a good number that translates well to the field ;).
So as I said a couple of times, some of my techniques might fly in the face of what you have read before or how you like to do things, and that is fine, these are lessons I have learned over a lot of flying and hours at the field that have worked for me for a very long time.