Though you have a capacity rating for the battery, you dont have a current at which you want to convert (like steve asked) we need to know if your solar panel outputs .5,1,5,10,3000 Amps, and what type of battery that you are using?
do you need 4,4.2 or 4.5VDC? 4 is not a common value for a battery voltage, 4.2 is seen occasionally, and 4.5 is quite common (using battery packs with multiples of 1.5V)