Just check coupons out (with price alert and history). You probably want to know what is the best price?
Size 282X 105 X 35±0.5mm, Indicator light Battery type identification / fault indication / full charge indication, DC 4.20V 250mA (3.7V lithium battery / 1.5V constant voltage battery without charge management), Model BST-U12, Weight 363g, DC 1.53v 350mA (Ni MH battery), DC 5.0v250ma (with charge management 1.5V constant voltage battery), Input AC 110-240V 50/60Hz
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 and price update (UTC):
Banggood
Banggood warehouse is located in China. So I have checked for active coupons (all category coupons and old ones), but there was no working coupon in Banggood.
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
Old coupons (from the oldest to the newest): BGTORCH, bGhOnEy10, bgshOOp10, BgoFErTaSchInA10, BgcLuBofErtA10, BGFLS15, BGAFF10OFF, BGCuponation10, 4BLF, BGHONEY2110, BG10OFFAFF, BGwhielabel, BG10OFFAFF1, BANGGOODSD, 6GSGIT, BGTorch4, 00c906
(these codes were not working in latest coupon update, but you can check them out anyway)
Price history and price alert
Here is price history (for all/most countries) for BESTON U12 AA Li-ion Ni-MH Battery Charger.
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)).