I’ve used a few different batteries for powering the goggles in the past, none of which were amazing or stood out as excellent performers. The Tattu 2500mah 2s pack worked great for the first few months but I rarely use it now as its lost a lot of its life. The original battery that came with the FatSharks were OK, they just did not have the capacity that I was looking for (or anyone for that matter).
Since I vape, and have plenty of the 18650 style batteries lying around I figured I’d give the official 18650 case a try after seeing it on eBay for $17.98 with free shipping. Seems like a great deal, the link below may not work by the time you read this, however, just search for the model number FSV1814 or use this link which should always work: https://www.ebay.com/sch/i.html?_from=R40&_nkw=FSV1814&_sacat=0&LH_TitleDesc=0&LH_FS=1&_sop=15
I have also used the adapter cables that are capable of taking 3-6s, which are great, and I use them as a last resort when my batteries die when out flying. Just not a big fan of having a wire coming off my face and getting in the way.
There are also plenty of alternative options such as the Furious FPV case pictured below, which is a bit more expensive but it also includes an on/off button. I would have went this route, but I already have done the “Power Mod” and added a toggle to my Fatsharks already.
You can always go the DIY route and build your own using 18650’s and even better if you have a 3D Printer handy and use one of the many designs available on Thingiverse. Check out all the designs available here: https://www.thingiverse.com/search?q=fatshark+18650&dwh=305cae23b0494d0
Anyways, for $17.98 I thought this was a great deal and wanted to share it.