If you have tools that are part of the Einhell Power-X-Change 18V battery platform, 1 battery and battery charger are enough. The 18-volt batteries are interchangeable, so you can power your radial arm saw, lawn mower, drill, and angle grinder with the same battery. You also only need 1 type of charger for this type of battery. This not only saves a lot of space in the shed, it also saves you a lot of money. The Power-X-Change batteries are available in different amperages.