Aliexpress
Click here… to search for 4x Sofirn 16340 900mAh Battery on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. There is one coupon available! Pretty cool, huh?
Link: Banggood product page
Coupon (19.33 USD): BANGGOODSD
(CouponsFromChina.com tip: you should apply the coupon in your 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): EYBG, BGBSPX, BGTORCH, BGSF, 502C6B, BGBFCR41, bGhOnEy10, BgcLuBofErtA10, BGFLS15, BG10OFFAFF1
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Price history (for all/most countries) for 4x Sofirn 16340 900mAh Battery is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).