Powerextra 1-Pack 4000mAh 18V Lithium Battery for Porter Cable 18 Volt Cordless Power Tools +Multi-Chemistry 18V Battery Charger for Porter-Cable 18-Volt NiCad NiMh & Lithium Battery - - Amazon.com
FYI, Porter Cable 20V Max and 18V Tools and Batteries are NOT Cross-Compatible
PORTER-CABLE 32-Piece 12-volt Variable Speed Oscillating Multi-Tool Kit with Soft Case (2-Batteries Included) in the Oscillating Tool Kits department at Lowes.com
PORTER CABLE PCCK600LB 20V MAX Lithium-Ion 1/2-Inch Cordless Drill with 2 - 1.5Ah Batteries - Walmart.com