speed controller capacitor


My 2000 DS 48v series cart seems to have an abnormal capacitor reading. The manual says that with the key off and the fwd/rev handle in neutral the reading across M- and B+ terminals of the controller, which shows capacitor voltage, shud be battery voltage which is 50v. It shows 25v. This is step 1 in checking controller output. Step 2 is with the key on and fwd/rev lever in Forward, the voltage across the same terminals should rise to battery voltage when the accelarator pedal is pushed to the floor,- which it does. Question what role does the capacitor play in the carts performance