Best Solar Battery

#1
I am hearing more batteries, but people guided me to use Solar power battery or lead acid battery. I planned to make a lithium battery pack for longer duration, but here the problem we see voltage drops continously.

Does someone tell me the correct information with guidence.
 
#3
For longer life use lithium batteries, but they also drops voltage slowly. If you are looking for a period of 3 years, then go with lead acid batteries as this is the best solution from my side.