Aliexpress
Click here… to search for Red 7.4V 1500mAh 2S 25C XT60 RC Battery on Aliexpress
Here are coupons that you can use.
Latest coupon and price update (UTC):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
Coupon (4.18 USD): BGee93d8
Coupon (8.94 USD): BG589b2e
(CouponsFromChina.com tip: you should apply the coupon in your 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): BG3bd2d0
(these coupons are old, so probably won’t work)
Price history and price alert
Price history (for all/most countries) for Red 7.4V 1500mAh 2S 25C XT60 RC Battery is here.
Price records source(s): Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).