send the entire radio system in for a checkup before you fly again.todays radios are designed to operate even if one cell in the rx pack goes bad.you may find that the tx battery could be the problem.I have sent systems in that were working fine for a checkup[preventive maintenance] only to get a system back that is back to factory specs and a bag of small replaced parts that were found to be bad some from the rx,some from the tx.