From the Bench – Lipo Batteries, C Rating, and Tips for Best Battery Performance

Old batteries available…free of charge… 😉

One of the questions I get quite often at events is what kind of batteries do I use in my aircraft.  I’ve been flying large EDFs and electric warbirds for a long time and good quality batteries are essential to performance.  There are tons of choices out there and so I thought I’d provide a little discussion on the batteries that I currently use and what I go for in terms of C rating.  There is most certainly a balance between efficiency and performance due to the extra weight of higher C rated packs and so this is worth discussing along with some of the general practices to use in maintaining battery performance because a well kept battery is a good performing battery.

As we get into this, I want to mention up front that this discussion is all based on personal experience and practical use in the field using all sorts of batteries over the last decade or more.  I don’t do any heavy side by side current testing or voltage testing or anything like that.  I’m simply relaying what has worked for me and the batteries I’m happy with.  At the end of the day, the best batteries and methods are the ones you’re happy with and work for you.

 

WHAT BATTERIES DO I USE?

First off to answer the question of what batteries I use, for the last 2 years or so I have been exclusively using Roaring Top batteries.  I’m sure you’ve been seeing them in some of my previous content.  I started out trying a couple packs in some airplanes and I have since converted everything over to the Roaring Top packs and I have been extremely happy with them.  The build quality is extremely nice and the performance is excellent.  Also, for a given C rating and capacity, I have found that the batteries are actually lighter than what I had been using previously for the same capacity and C rating.  So, not only was I getting good performance from the packs, I was getting a weight savings as well.  So, it was a win-win in that respect.

As mentioned up front, I don’t do extensive side by side testing, I simply use the packs in their intended use in my airplanes and see how they hold up as I fly and use them.  Based on that, I can say that the Roaring Top packs have held up fantastically!  I have found these packs to be the lightest of all of the brands I’ve used to date for a given C rating and I’ve used all sorts of brands.  The packs have also held up fantastically over numerous cycles since receiving them, where I’ve had other packs start to get a soft over time as I use them.  I’ve been using the same packs for the last 2 years and they all still look brand new!

HOW MUCH C RATING IS TRULY NEEDED?

One things that is really worth talking about is C rating because I think there may be some misconceptions out there.  For me personally, I primarily fly 35C packs and many folks are actually surprised by that.  The thing is that just because you can get a 70c pack doesn’t necessarily mean that that’s what is required for optimal aircraft performance.  I say that because yes, higher C rating does mean lower internal resistance in the battery and cooler battery operation, but it also means higher battery weight.  So, there is a balance here.

So, first off, let’s talk about what C rating truly means?  It’s intended as a simplified metric to provide the maximum performance capability of your battery.  A way to know how many amps you can pull and not completely destroy the pack.  For example, let’s say you have a 35C 5000 mah pack.  That means that the maximum recommended amperage for the pack is 175 amps.  That’s 35 times the battery capacity in amp hours (5.0 aH * 35).  So now, if we have a 70C 5000 mah pack, that means a capability of 350 amps. The thing to keep in mind is that most electric setups aren’t pulling anywhere near 175amps let alone 350amps!  Obviously, the closer you are to that maximum, then the less margin you’ll have, the hotter the batteries will get and the more likely the battery won’t hold up over time.  So if you have a system pulling close to that max capability, then you definitely need that higher C ratings or a higher capacity battery.  Again, it’s all about finding that balance and knowing that the system needs and also what you’re wanting for flight time too.  I realize too not all manufacturers accurately label their packs too, so having margin is always good.

A big part of this equation is capacity.  Let’s say you have a system that pulls 100 amps, the smaller capacity pack you are using, then the higher C rating will be required.  However, you can mitigate this with more capacity which also will increase your flight time (and weight).  For me, my goal is to fly as high a capacity as is practical for a given airplane to maximize the flight time.  I rarely fly capacities less than 5000 mah unless I’m flying smaller airplanes.  So, that is another reason why I lean towards the 35c packs since I don’t have any airplanes pulling anywhere near 175 or more amps and so I can save weight on these higher cap packs.  In my Freewing jets, I’m using 5800s, in my larger jets, I’m using 6200s on up to 8000s depending on the size of the airframe.  8000s are ideal in a really large high powered EDF if they will fit into the airframe and it can handle the weight.  For a system pulling 120 or more amps, you can get 5+ minute flight times pretty easily with those large capacity packs.

So, this is the approach I like to take.  Ultimately, the best batteries are the ones that give you the power and flight experience you’re looking for.  I like the 35c sizes based on the setups I’m flying and they offer a great balance between battery weight, aircraft performance, and flight time.  This goes all the way up to flying my high powered 120mm EDFs.  It really is all about balance and finding what works best for you.  One thing to keep in mind is that there is an optimal battery operating temperature which is typically between 80-140 deg Farenheit.  If you are outside that range, the batteries won’t put out power as well (yes you can have batteries that are too cold).  I typically will preheat my packs by setting them on the dash of my car before my flights which usually warms them up to a nice operating temperature for flying.  I can tell a notable difference between cold packs and pre-warmed packs in the aircraft takeoff performance.

 

BEST PRACTICES FOR MAINTAINING BATTERY PERFORMANCE

One of the other things that I wanted to cover are some best practices that have helped me get the most cycles from my lipo batteries.  It doesn’t take much truthfully, but there’s definitely some care in handling to ensure the batteries hold up and stay reliable and safe.  So mostly, I just have a couple recommendations I want to mention.  As we go through this though, the assumption is that you know how to handle and charge lipos.  However, I can’t stress enough that a mistreated lipo is an unsafe lipo that can result in fire and we definitely don’t want that!  It’s like when you’re opening a can of premade biscuits…you don’t know when that thing will blow!

The one big recommendation I have is to never let your batteries sit fully charged overnight.  Lipo batteries do not like to sit in a fully charged state, even if it’s just over night.  The least amount of time they sit charged, the better they will perform and maintain balance over time.  Also, they are more volatile fully charged, so it’s safer too.  For me when I’m heading to the field, I usually will get up early to charge batteries while I get my gear together and pack my car.  I also charge at the field as well.  This alone has really extended the life of my batteries.  The fact is that this is especially important when you’re dealing with lower cost battery brands as they usually aren’t perfectly matched out of the box and they will get soft on you quicker from sitting fully charged.  I’ve seen it happen from personal experience.

The other recommendation is to always, always check the battery voltage after your flights to know just how low you’re getting.  Typically anything above 3.7v/cell is ok, above 3.75v/cell is even better.  However, if you’re below 3.8v/cell, then I definitely recommend doing a storage charge on the batteries before packing them up for the day.  It usually doesn’t take that long and it is the best thing to do to help maintain battery performance.  I’ve gotten into the habit of doing a storage charge on the batteries after each flying session since I always bring my charge setup with me to the field.

Lastly, even though you can charge at higher rates these days, I recommend always charging at 1c.  If you have a good quality charger, you should be able to do a 1c balance charge in about 30-50 minutes assuming that they are mostly balanced.  The charger I have is the Revolectrix PowerLab Duo which I love.  With it, I’m able to parallel charge packs, even large capacity packs, usually within 40 minutes or so.  It has two sides to it too, so I will parallel charge packs on each side.  On a good day, I’ll usually charge up to 8 packs at once, 4 on each side.  Obviously, you don’t have to go overboard on the charger like I did, but I will say that one of the best investments you can make in this hobby is buying a good quality charger.  I will say, it is extremely nice to be able to balance charge a bunch of packs all at once in about 40 minutes.  It saves a ton of time, so the time to fun ratio is very good!

 

FINAL THOUGHTS

I’ve been wanting to talk batteries for a while, so am glad I could finally make it happen.  The best batteries are the ones you’re happy with and I’ve been really happy with the Roaring Top packs.  The build quality is great, they are light weight, and they put out great power.  The other part of this is battery care and handling.  Treat the batteries right and they will take care of you.  Also, in terms of storage, I recommend storing batteries in ammo cans with holes drilled in the top or also lipo sacks work too.  It’s all precautionary just to be safe.  Most problems are a result of either over charging or over discharging the batteries, so always keep an eye on the cell voltages.  Until next time, I’ll see you at the field!

 

8 thoughts on “From the Bench – Lipo Batteries, C Rating, and Tips for Best Battery Performance

  1. Great article on LiPo batteries Chris. I think I have been guilty of thinking I need higher “C” ratings. I will consider your thoughts as I move forward in the hobby. Thanks for being a great ambassador for the hobby.

  2. I`ve been trying to tell people that very thing for years. Most guys think you get a performance increase with higher C rated packs ,not necessaraley so. You can only draw what the sys.is capable of drawing, Why a 70C pack? if you could draw that much amperage the solder joints are approaching melt down.
    I agree with your logic and your choice of packs.

    • Yeah, it gets to a point where you’re only carrying around dead weight. There’s always a compromise. Thanks for commenting!

    • I did, it’s on the list for shipment. Based on the demand, it’s been taking me a bit longer to get orders shipped. Sorry about that!

  3. Chris this is awesome information. Weight is the enemy and I didn’t realize that these super cool (and heavy and expensive) 70C packs are overkill. Now if I can just get the replacement board for the centerburner I destroyed, (this time hooking up a 2s pack as is CLEARLY stated in the instructions:() Thanks again for all your great info.

    Matt

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