explain this.....

[bionology]

(j) state the possible advantages of developing other types
of cell, e.g. the H2/O2 fuel cell and improved batteries (as in
electric vehicles) in terms of smaller size, lower mass and
higher voltage.

I didn't get the second part of the improved batteries, anyone can explain?

 

[beacon_of_light]

Improved batteries here could mean "longer-lasting" or " pollution-free" ... and the question itself says " in terms of smaller size, lower mass and higher voltage" these are some improvements to the cells/batteries...