Med, you find out by looking it up. Your engine maker should have a manual and a part number for the starter--that should (nasty word) say how much power it consumes. If not, contact whoever makes the starter, they can tell you. If you had to make a blind guess you could look for the wire size leading ot the starter, or any fuse in the starter cable, and ballpark down from there but that's a rough way to do it. (There are ways to measure it with a meter but unlikely you'd have access to one in that power range.)
As to the battery, same thing. Call the maker or look to their web site, the information is usually available even if it isn't on the web.
And of course bear in mind that also depends on "fires right up" versus the higher load of "needs to crank for fifteen seconds" which will generate a whole lot more heat in everything powering it.