$9.99 – 5V LCD Display 18650 Lithium Battery Capacity Tester (Banggood, Aliexpress: 5V LCD Display 18650 Lithium Battery Capacity Tester Power Detector Module 2 Way with Charging Discharge Type-c Port (the best price with coupon)).
You can get 5V LCD Display 18650 Lithium Battery Capacity Tester for $9.99 with coupon (from Banggood). Go down and check coupons out. Remember to check price history if it is available. Best price?
Latest price update (UTC time):
Banggood ($9.99)
Banggood warehouse is located in China. Hmmm… There is no active coupon in Banggood at this moment. The question is – is it a good price? Pretty good price – average ($10.24) is higher than current one!
Link: Banggood product page
Price: $9.99
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/feV
Old coupons (from the oldest to the newest): BG589b2e, BG5c1899, BGcbd315
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Aliexpress
There’re some similar (or not) items on Aliexpress
You can use link bot to get even lower price:
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 5V LCD Display 18650 Lithium Battery Capacity Tester. The lowest price was: $8.99.
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)).