LiPo chemistry is designed for applications that need a higher sustained voltage. LiFePo4 chemistry is designed for applications that need higher sustained current. I have found that 2S LiPo's avoid the high voltage errors that I was getting on some of the Jetcats, I have had, with LiFePo4s. But, LiPos also do not provide the current needed for starting once they have used about 50% - 60% of their supposed capacity. It appears that they just can't deliver the necessary current for a kero-start, at that point. If your turbine won't start after a couple runs/tries, the first thing we end up doing is changing the LiPo battery and frequently it will then start. Put the replaced battery on the LiPo checker and it says you still have 40% capacity left.
The new brushless starters on some of the Jet Centrals are using huge battery capacity. We have a couple pilots here that can only get 2 starts/flights on a 2000+ mah LiFe battery. They used to get 4 before JC put on the new starters. These guys are NOT happy. These folks may need to give LiPos a try. Or, put in some larger capacity batteries.
I find that I can get 5 K-160 starts and flights with my 2100 mah LiFePo4s. Never tried for 6. But I usually end up putting ~1600 ma back in on a charge. My 2700 mah LiFePo4 gives me 6. Never tried for 7.
On the P-100, I use 5700 mah 2S 30C LiPos. I can easily get 10 starts and flights on those. The P-100rx is a very efficient turbine. Starts quickly and uses little fuel for the amount of thrust it provides.
The P-140RXi is about the same as the P-100 on battery consumption. But, I am using LiFePo4 for the turbine. Only thing, it is a fuel hog compared to my old P-140rx.
I never charge LiPos in the planes. I have had one member lose a couple planes due to a fire while charging LiPos in the plane. I also saw one this year almost burn down cause the charger was set wrong (i.e. set tp pB versus LiFe.). Lots of smoke and a little fire! I just make sure I can easily pull them out for charging. I always use 2s LiPos on the receiver packs anyway, because I use high voltage servos and Rxers, etc.. As long as you have to take out some batteries anyway, I set the plane up so I can easily get at all of them. I know some planes do not easily allow this. So far, I have avoided those planes.