Weight After Packaging 295G (Subject To The Actual Product), Wire Length About 3M, Plate Weight About 193G (Subject To The Actual Product), Size 175 * 115 * 10Mm, Material Grade A Monocrystalline Silicon Solar Panel, Short Circuit Voltage 6.2V, Package Size 200 * 128 * 73Mm (White High-Grade Neutral Box), Working Voltage 5V (Charging 3V-5V Battery), Short Circuit Current 750Ma, Interface Micro USB (Android), Power 4W, Working Current 0-800Ma.
Go down and check coupons out. Remember to check price history if it is available. Let’s see what best price is ATM.
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 price update (UTC time):
Banggood
Banggood warehouse is located in China. Only one coupon available!
Link: Banggood product page
1. ($22.49): BGAMMT03
this code has to be applied in your 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): BGa46747, BGCarEle4, BGissam740, BGSCM11, BGCarEle5, BGLMQ15
(these coupons are old, so probably won’t work)
Price history and price alert
Check out price history chart (for all/most countries) for 4W 5V Solar Panel Charger Micro USB. The lowest price was: $12.99.
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)).