Help troubleshooting a voltage monitor/alarm. Charger says 4.19v across the battery, $3 monitor reads from 4.13v to 4.22v

I bought a couple inexpensive low voltage alarms from a distributor on ebay, but I’m having issues trusting their reading. Does anybody have any alarms that are accurate with what their charger claims? I have a lot of faith in my turnigy accucell charger, though Im totally open to learning that the charger is reading inaccurately too. I’m very new to DIY and need help figuring out if its actually my alarms that are cruddy or if my charger is whack and overcharging. Thanks in advance guys!

I also bought 2 cheap lipo beepers when i started my build. Stopped using them after a few days because they both showed crazy voltage drifts in my all new turnigy lipos.

Got a refund from the seller and now im just using the VESCs battery cut off start and end feature to safe my lipos because i never notized considerable drifts when i plugged in my Imax B6 charger after my rides.

Glad i’m not the only one. I guess it’s normal.