I've been looking for alternatives to Nikon batteries and found few. This one seemed particularly interesting as it can charge more batteries than Nikon's original. Tested on my old Nikon SB900, everything works. It's a lot more than I imagined. However, it is not difficult. Build quality is decent, but I'm not sure it can last longer than Nikon's. Rarely used though as I've found that black eneloop batteries are still enough to cover a 2-3 hour session, using this only as a 'just in case' scenario.
10'' LED Ring Light With Tripod Stand & Phone Holder For Live Streaming/Photography, Dimmable Selfie Makeup Video Recording Light With 3 Modes & 10 Brightness Levels
13 Review
YONGNUO YN660 Speedlite: Versatile Wireless Manual Flash with GN66 Power for Canon Nikon Pentax Olympus
10 Review
Canon 600EX RT Speedlite Flash Black
10 Review
14 Review