Quality of meat is extremely important in making moist & juicy slow cooker chicken. My favorite chicken to use comes from ButcherBox.  ButcherBox has only free range, certified organic chicken that is humanely raised with zero antibiotics or added hormones. To avoid dry and mealy meat the best tool you can add to your kitchen tool box is an instant-read thermometer.  At the two hour mark, check your chicken for temperature. Cooked chicken has a temperature of 165F. If your chicken maintains a temperature at or above 165F, it is done. It also helps to allow the meat to rest and then cut against the grain prior to serving.