Battery: built-in 200mAh Li-ion battery, Duration of use: standby for 20 days, Charging time: 2 hours, continuous use more than 500 times, Product material: ABS and PC.
Check coupons or create price alert down below. Do you want to know what the best price is?
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. There is no active coupon in my database right now (for 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!
Additional Banggood coupons: first page and second page
Old coupons (from the oldest to the newest): TTxBG10, aff7off, bgssaff9, AFfbG10, 502C6B, BGBFAFF2019, BGCITYADS2019
(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 TDS TOC COD Spectral Water Quality Detector. The lowest price was: $39.09.
Price records source(s): Gearbest, 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)).