Lowes offers Kobalt 24 -Volt 1 -Pack Lithium for $39 (reg. $69.98) free shipping. 

Product Description:
Kobalt 24-volt max 4.0-Ah Li-ion battery provides more power and runtime, so you can get the job done fast. The power indicator keeps you informed as to how much battery is remaining before needing to be charged. The battery monitoring and protection system prevents the battery from overheating.