What size battery is recommended for a RYOBI Saw?

Battery Recommendation for Optimum Performance 

For best runtime and performance, it is recommended to use a 4.0Ah battery or higher, such as: 

• 18V ONE+ 4.0Ah Battery (RB1840C) 
• 18V ONE+ 5.0Ah HP Battery (RB1850X) 
• 18V ONE+ 8.0Ah HP Battery (RB1880T) 

Smaller batteries can be used; however, they typically provide reduced runtimes and lower performance levels.