The Sennheiser BA 70 is the rechargeable lithium-ion battery pack for the Sennheiser Evolution Wireless Digital (EW-D) range. It powers the EW-D SK bodypack transmitter and the EW-D SKM-S handheld transmitter, replacing two AA batteries and giving users a reusable power source that can be recharged many times. Using rechargeable packs is cheaper and more reliable than disposable batteries for venues, churches, schools and rental companies that run wireless microphones every day. The pack is rated at 3.8 V and 1.72 Ah, weighs 57 g and measures about 54 x 30 x 15 mm. One battery is supplied. For charging, Sennheiser offers the separately sold EW-D charging set and L 70 USB charger, both listed alongside it as related accessories.