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 (29.99 USD): BG95279
Coupon (31.67 USD): BG10OFFAFF
Coupon (31.67 USD): BGwhielabel
Coupon (34.19 USD): 13f142
(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): bGhOnEy10, BG3412, BGCARELEC, BGINMO, BGAFF10OFF, BGCuponation10
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Price history (for all/most countries) for MDXT-600 12V 24 V Car Battery Tester is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).