Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in Hong Kong. There is one great coupon!
Link: Banggood product page
Coupon (23.24 USD): 2022ACTIESNL
(CouponsFromChina.com tip: apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): f62884, aff7off, BGCCOO, bgssaff9, BGBCFPV, BGBCBG10, bgchinafest, 502C6B, BGOTC21, BGBFAFF2019, BGCITYADS2019, bGpAnDacHeCk, BG9NY, 2020CNY, BGMPB2020, BGAFF7OFF, bGhOnEy10, BGSS10%SW, bgshOOp10, BgoFErTaSchInA10, BgcLuBofErtA10, BGAFF10OFF, BGCuponation10, 13f142, BGHONEY2110, 00c906, ADMITAD2212
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for Fatshark 7.4V 18650 RC Battery Case.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).