Output Power: 5W, Working Time: about 3-12hours, Working Temperature: 37-50℃, Input Interface: TYPE-C, Input Charging Current: DC 5V-0.8A, Material: ABS PC, Charging Time: about 6hours, Battery Capacity: 3900-4000mAh.
Price history, coupons and price alert are available on this page. What is best price?
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.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China. You can get coupon down below.
Link: Banggood product page
1. ($27.89): PICODICOM
apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop.
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): XMIF25, BGMumlatzimF5
(sometimes old coupons work, so you can check them out (this site checks them on every price update))
Price history and price alert
Check out price history chart (for all/most countries) for Xiaomi Solove F5 Desktop Fan 4000mAh. The lowest price was: $16.07.
Price records source(s): Gearbest, 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)).