The e-box has two metal posts that stick up. The e-box is the plastic box where your spark plug wires originate from. They are for attaching your spark plug boots to when they are not on the spark plug. It grounds them. It wont make the engine crank faster but it will prevent the boot from making an arc that might shock you, ignite gas fumes, or damage the coil.
I get my batteries from walmart too. They are fine.
Maybe try a different compression tester. The big auto parts stores will do tool loaners with a refundable deposit. If you really only have 95 psi, then that's pretty low. It might keep it from starting. Maybe put a little 2 stroke oil into the spark plug holes and crank it over some more. If the skiis have been sitting, there could be some rust on the cylinder walls. The oil could lube it up and make it crank faster.
No need to take off the exhaust pipe if you are trying to remove the carbs. The carbs come out from underneath the pipe. Assuming the air box is off. Remove the return fuel line gently because the plastic nipple can break off (thats the fuel line on top that you can see). The pulse line should come off easy( thats the most forward line). You have to feel for the four allen head bolts (6mm) that hold the carbs. Remove carbs and lay them in the bottom of the hull. Then...Remove the cable nuts on the carb side of the brackets so you don't have to re-adjust your oil pump, throttle, and choke. Take the straps off your oil tank and move it forward a few inches. Unhook the fuel inlet line(thats the one you can't see from the top). The carbs then come right out. You might want to pick up a package of rubber vacuum caps to put over the return nipple and inlet nipple as soon you've removed the lines. That will keep gas from spilling out because you have to turn the carbs sideways and upside down to unhook the cables and to maneuver them out.
Before you do all that though, did you put a little premix down the carb throats to see if it fires? Also, did you verify that it has spark?