8 You can have alternator belt slippage without noise, which means the alternator isn’t spinning fast enough to keep your battery charged. Remember, your alternator puts a significant load on the belt and engine, which means belt tension must be within limits at all times. Belt tension should be a 1/2 inch of play each way. Ford wants you to have 60-90 pounds of belt tension for sixes and 80-110 pounds for V-8s. One clue of belt slippage is a hot belt and pulley right after shutdown.