I’ve found the Charge 2 and HR chest strap to be really quite close. I normally find there is a difference of 2/3 bpm, however I do find that the Charge will sometimes lose track or suddenly drop/spike bpm but that’s the nature of a wrist HR tracker, its going to move on your wrist especially during exercise. Maybe if the Charge was on a elastic strap instead of a rubber strap that might help.