Stop take a break and grab a beer... or 3
Do you have a volt meter? A cheep DC meter can be bought at Harbor Freight, Auto Parts store, Walmart etc.
Turn the meter on, and turn the switch to DC _ Volts (DCV)
Place the red lead on the + of the battery
Place the black lead on the - of the battery
Do you read 10 - 12 vdc --- Yes move on, no replace the battery
Leave the black lead on the battery, and move the red lead to the rear E-Box where the starter solenoid is. (trace the big red wire). Do you have 10 - 12 volts (same as above) on the big lug of the solenoid ---- Yes move on, no replace red lead
Place the red lead on the positive on the battery, and the black lead on the engine block, somewhere where there is no paint. Do you have 10 - 12 volts (same as above)
Look on the negative post of the battery, are there 2 wires on it? a big and small?
Report back, and we can move on... The group here knows a lot on these skis