In this video the best battery for Solar PV systems is explored. There are a wide variety of batteries in the market, each suited for a particular application.
For solar PV systems mostly car cranking battery is used which is the worst possible choice for that application. In the developing world truck batteries are used for higher storage capacity which again is a poor option.
Another battery that is making waves is the saltwater battery which is also examined in this video.
Cheapest Lithium Ion batteries: