About the batteries in CubCrafters CC11 family aircraft (Carbon Cub and Sport Cub)
In the interest of saving weight, and since batteries are notoriously heavy (most of them contain LEAD for heaven's sake!), batteries are an opportunity to save some easy weight. In our quest for light weight we are therefore using the smallest battery we can to get the job done -- a motorcycle battery. Starting a 340 cubic inch engine with a motorcycle battery pushes these powersports batteries to their limit. For a short time we switched to an AGM battery and found out it wasn't up to the task so we replaced them all and went back to the sealed lead acid. Because of the strain we put these batteries under their life is shortened. Personally, I recommend replacing your main battery every other year at annual regardless of how it is performing just because of the stress they are under.

In our quest for both improved starting performance and weight reduction we have been evaluating the Shorai Power LFX18 LiFe (lithium iron phosphate) for nearly a year now. We are VERY attracted to the weight savings which is over 5 lbs, in our world that is very significant, as well as the apparent improvement in starting performance. On our company planes they have worked perfectly, both saving weight and in improved starting performance. Our original Carbon Cub SS, N155PC, failed to start on me twice while hot over the years and stranded me when my attempts at hand propping then failed. It got so bad that when taking that plane cross country by myself I started carrying a little rechargeable jumper battery. I can hand prop a CC340 by myself maybe 40% of the time, the other 60% I am stranded. Since installing the LiFe it has always started perfectly cold or hot to the point that I no longer carry the jumper when taking trips in it. A couple of our owners have also tried them and not had good luck, I have no explanation for that.

Bottom line: we would have already switched to LiFe if we could find better test data on failure modes. As the aircraft manufacturer we simply can't have batteries exploding under the pilot's butt and we can't find enough empirical test data yet to have that level of confidence. Performancewise we are convinced, some contrary owner experience notwithstanding, and we are continuing research in this area.

Things you can do to improve starting performance
If you are experiencing difficult starts, hot or cold, there are some things you can do to optimize starting performance. Since our starting systems need every fraction of an amp our batteries can deliver we need to make sure the current makes its way as efficiently as possible to the starter. To accomplish this go to any auto parts store and get some dielectric grease, here is an example. Then find yourself a maroon Scotchbrite pad which can be found in the aviation department of Home Depot. Now, wait for a Saturday when it is IFR and you can't fly and spend the rest of the day in the hangar. Starting from the battery, dissasemble each connection in the fat wires, both positive and negative, from the battery to the starter. Take a scotchbrite pad and buff the mating surfaces so there is no corrosion or contaminates, just fresh metal, and smear a very small amount of dielectric grease on the mating surfaces. Reattach the connection with the appropriate torque. This is like a chain, if you miss one connection (link) your path is still weak. Remember to include both the positive path all the way to the starter and the negative path all the way to ground. Don't forget the starter ground and the engine ground strap. Now you have optimized the electrical path and will get nearly 100% of the available battery current with minimal loss. Gary, you live in a moist environment, you might have the most to gain from this drill.

Hope this helps shed some additional light on the issue, and we will keep everyone posted in our quest for improved battery performance, we appreciate you doing the same.