Heavy duty 9 volt Lithium battery for Marshall 5 & 10 channel receivers only. (Two 9 volt lithium batteries are required for Marshall receivers. These are long life Lithium batteries and they will last up tp four times longer than an alkaline battery. Use the 9 volts for the older style 5 & 10 channel receivers only. NOTE: THE NEW FM-1000 RECEIVERS TAKE 6 TRIPLE A BATTERIES PER RECEIVER.