New 6ah HP batteries are smaller, same size as old 4ah : r/ryobi
Ryobi PSK006 ONE+ 18V Lithium-Ion 4Ah Battery (2 Pack) & Charger Kit NEW IN BOX 33287197309 | eBay
18V ONE+ 4Ah LITHIUM-ION BATTERY - RYOBI Tools
Power Tools Batteries for Ryobi 18V 4Ah Battery Replacement - China Power Tools Battery and Ryobi 18V 4Ah Battery Replacement price | Made-in-China.com
One World Technologies Recalls Ryobi Cordless Tool Battery Pack Due to Fire and Burn Hazards | CPSC.gov