Cordless hand held trimming systems. What's so special about lithium-Ion batteries?

Lithium-ion batteries are rechargeable, low weight, high performance and have a much shorter charging time than conventional batteries. 

They also, have little or no discharge when not in use, making them very convenient to store and use again. 

Some cordless shears can take as little as three hours to fully charge from empty and run for as much as 1hr 40 minutes.