Basically copy coupon, view price history or create e-mail price alert. Do you want to know what the best price is?
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest coupon code price check (UTC time):
Constant Current 2Ax1 / 1Ax2 / 0.5Ax2, Operating Temperature 0-40℃, Size 110x53x30.5mm （LxWxH）, End-of Charge Current ≤150mA, End-of Charge Voltage 4.2±0.05V/1.45±0.1V, Brand XTAR, Weight 62g, Model FC2, Input DC 5V 2A
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($7.99): BGFC22
2. ($19.30): BGTorch4
this code has to be applied in your cart after clicking “Proceed to checkout”. Click to copy code and open shop.
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Old coupons (from the oldest to the newest): BGwhielabel, FIN0905, 4BLF, BG10OFFAFF1, BANGGOODSD
(these coupons are old, so probably won’t work)
Price history and price alert
Here is price history (for all/most countries) for XTAR FC2 Battery Charger.
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)).