According to my DB the lowest price is $8.45 for ANENG BT-171 Battery Tester 12V (in Banggood). Price history, coupons and price alert are available on this page. Best price?
ANENG BT-171 Battery Tester 12V LCD Digital Auto Battery Analyzer Charging Cranking System Tester Car Battery Checker Diagnostic Tool
Latest coupon and price update (UTC):
Banggood ($8.45)
Banggood warehouse is located in China. I’m afraid that there’s no working coupon in Banggood. Is it a low price? Hmmm, price is higher than average (which is $7.74 right now), so better set price alert down below…
Link: Banggood product page
Price: $8.45
Old coupons (from the oldest to the newest): BGM1TOOLS88
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Price history and price alert
Here is price history (for all/most countries) for ANENG BT-171 Battery Tester 12V.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood and Aliexpress (only if product name will be the same as on Banggood and I will post it on social media though, so it’s more like Banggood price alert)).