That is a broad question....
I'm finding that you use choose Cells/Battery based on what you want your out come to accomplish.
All Cells/Batteries need understanding for safe use. LiFePO4 can be safer than other chemistry's.
These are some that are mentioned in this forum often:
Lipo: Turnigy, Zippy
LiFePO4: Ping, A123, Headway
You have to know specs of each of these and choose what you might need to accomplish your specific goal.
I use Headway individual Cells so I can determine the voltage/load for a given build. If a cell fails, easy for me to fix.
If they actually charge 2,000 times, then great value in the long run.
I use 76.8nom 8ah (24 cells) in my back pack.
It weighs 20lbs. It will take me 30km distance at 80% DOD. Work is only 12km away so I can charge at work with less than 40% DOD
or commute both directions under 80% DOD. After seeing Low Racer, look up YouTube Chris Luxemburg, Lipo pack catching on
fire, I decided that I would not put Lipo in a back pack.
If I use Lipo, I will put it in Metal Case and have a quick release system
to separate it quickly from ebike incase of fire.
I like the back pack because it adds stealth to the ride.
There are those here that are Lipo users for many reasons. Read read read!
I believe that these are 500 charge. Many here have used Lipo safely and with no fire for many charge/discharge cycles.
Knowledge is the key. Self educate as much as possible and the possibilities are some what endless!
Tommy L sends....