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.
Just check coupons out (with price alert and history). Do you want to know what the best price is?
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 and price update (UTC):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
1. ($27.89): PICODICOM
put item in your cart and apply coupon code there 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
(system checks these coupons on every price check (like once per 24 hours), but you can check them out anyway)
Price history and price alert
Here is price history (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)).