Aliexpress
Click here… to search for 5x 3.7V 150mAh 20C RC Battery and Cable on Aliexpress
Here are coupons that you can use.
Latest coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (12.62 USD): AFfbG10
Coupon (13.04 USD): aff7off
(CouponsFromChina.com tip: apply code in your basket (cart) after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): rchobbies8, TTxBG10, e2bcea, 502C6B, BGJJRC10, BGBFAFF2019, BGCITYADS2019, BGVDay10%off
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Price history (for all/most countries) for 5x 3.7V 150mAh 20C RC Battery and Cable is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).