Basically copy coupon, view price history or create e-mail price alert. Let’s see what best price is ATM.
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):
[EU Direct] FOSSiBOT FB3840 Expansion Battery / 3840Wh LiFePO4 Battery Pack for F3600 Pro / USB-A 18W / Type-C 100W / 200W Max Solar Charge – Set 1
Banggood
Banggood warehouse is located in Europe 
. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood. There’s only 1 record in my database, so I have no idea if the price is OK.
Link: Banggood product page
Price: $-3
It looks like this item is out of stock in Banggood. If you found it then please send me the link. I will replace it.
Click here to search on Banggood!
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k and https://couponsfromchina.com/short/5cd
Price history and price alert
There is only one database record (it was for $1509.89), so you can’t see price history chart.
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)).