Go down and check coupons out. Remember to check price history if it is available. What is the best price?
Aliexpress
There’re some similar (or not) items on Aliexpress
Click here to search by yourself. Here are coupons that you can use.
Latest price update (UTC time):
high thermal conductivity aluminum alloy, Charging time 2 hours, Charging input 5V/2Amax, Green, Color Pink, Size 63mmx 900mmx 33.8mm, Product model T-40, Material Fire grade ABS, Heating temperature 52°C, Red, Electric core energy 5000mAh, Product name 52° hand warmer power bank
Banggood
Banggood warehouse is located in China. There is one great coupon!
Link: Banggood product page
1. ($24.99): BGbeauty001
apply it 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): vipupgrade8, BGMi2i, BGoo1, BGHHH2, BGOMG23, BGHB20
(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 Maoxin 52C Hand Warmer 5000mAh.
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)).