Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (17.78 USD): Cuponation9
Coupon (17.98 USD): BGRCParts8
Coupon (17.98 USD): TTSUMMER8
(CouponsFromChina.com tip: put item in your cart and apply coupon code there 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): 18650, e2bcea, AFfbG10, BGAFF10OFF, BGTT10, bGhOnEy10, BGBC1, BGdragonBoat, BGRCBC7, BGRC902, BgoFErTaSchInA10, BgcLuBofErtA10, 13f142, Parts8, BGRCBC11, BGGAL8, BGSFBC1, Tabby20, BG1efeb0, 8Couponsde, MVC8SPRING, 8BGwbg2204, tRaDetRaCKeR, 8wEbgaInS5, pROMo8cuPoN, BG8RCToy, BGJUNEGSG9, BGRCT10, BGISDTA406, 9OFFSUMMER
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Do you need price history chart (for all/most countries) for ISDT A4 10W Battery Charger? There we go.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).