Ebay offers Open-Box Greenworks 24V Powerall 4.0Ah Lithium-Ion USB Power Tool Battery for $26.99 (reg $89.99) with free shipping.

Product Description:
The Greenworks 24V POWERALL lithium-ion platform powers over 125+ indoor and outdoor products, including lawn mowers, blowers, string trimmers, chainsaws, power tools and more! The 24V lithium-ion battery provides 20% more power and 35% more run time while delivering fade-free power with no memory loss after charging.

• Dimensions (Overall): 2.8 Inches (H) x 1.8 Inches (W) x 5.2 Inches (D)
• Weight: 3.1 Pounds
• Volts: 24 Volts
• Battery Capacity: 4000 (mAh)
• Assembly Details: No Assembly Required
• Package Quantity: 1
• Compatible With: GreenWorks G-MAX Products