 "GoPro Dual Battery Charger + (for HERO4) - AHBBP-401"@en AHBBP-401 Filmtools"@en
"
Charge two HERO4 batteries simultaneously
Power it with most standard USB power adapters, the GoPro Wall or Auto Charger, or a computer
Dual LED indicator lights 
Includes a spare 1160mAh lithium-ion rechargeable battery 
"@en 
 "GoPro Dual HERO System for HERO3+ (Camera not included)"@en-US "Accessories - Page 791 | EISF"@en-US
"Capture a wide variety of content with the Dual HERO System. The tandem housing holds two HERO3+ Black Edition cameras (sold separately), enabling you to capture full-resolution videos and/or photos simultaneously with uncompromised image quality. You can also record synchronized footage to convert to 3D using free GoPro Studio editing software. Waterproof to 197'/60m. Compatible with Hero3+ Black Edition Cameras ONLY"@en-US 