Best Solar Battery

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.
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.