Does anyone know how long the battery in the HF coil is warrantied? My ORX with 9" round HF coil was purchased in Jan 2020. I only hunt about once a week for 3-6 hrs. The battery in my HF coil only holds a charge for about 6 hr. The manual says it should hold its charge for 20 hrs or more depending on freq. used. Have any of you had this issue? Thanks