Color: Black (The red transmitter also can use black color. It will get another new view.), Design for 18650 Battery, Item name: Battery Cap, Suitable transmitter: Taranis X-Lite, Brand name: Frsky, Quality materials with a glossy surface treatment.
Basically copy coupon, view price history or create e-mail price alert. What is the best price?
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 coupon code price check (UTC time):
Banggood
Banggood warehouse is located in China.
Link: Banggood product page
1. ($17.99): bGhOnEy10
2. ($17.99): BGTT10
3. ($17.99): BGSS10%SW
4. ($18.59): BGAFF7OFF
put item in your cart and apply coupon code there 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): BGXLiteCap, aff7off, BGXLCap, BGfrsky10, BGaDmITAd, BGRCCD30, BGFRSKY15, bgchinafest, FBCOUPON1
(I don’t think these’re gonna work, but you can try ’em out anyway)
Price history and price alert
Check out price history chart (for all/most countries) for FrSky Taranis X-Lite RC Battery Cap Pair. 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)).