What was found
AT 38000 FT WE WERE DIVERTING AROUND WX NEAR. WE HAD LARGE LIGHTNING FLASH & SHORTLY AFTER C APTAIN SMELLED ACRID SMELL & THEN THE COCKPIT STARTED TO GET SOME SMOKE. BEFORE WE GOT MASKS ON THE SMOKE SCENT WAS GETTING STRONGER. WE DECLARED EMER & GOT VECTORS & DESCENT TO CLOSEST FIELD. FIRE DEPT MET US & SAID NO VISIBLE FIRE. PARKED ACFT. ARRIVED AT ACFT DISCOVERED A STRONG ACID SMELL IN COCKPIT. SUSPECT COMING FROM SHIP BATTERY. LIGHTNING STRIKE INSPECTION IN PROGRESS. LIGHTNING INSPECTION COMPLIED WITH 05-51-19-2 NO DEFECTS NOTED. R & R MAIN BATTERY DUE TO STRONG ODOR IAW 24-3 1-01-4 & R & R BATTERY CHARGER IAW 24-31-02-4 OPERATION S NORMAL. BITE TEST OF BPCU IAW 24-41-03 NO FAULTS FOUND RT & ENG PER JRH & PERFORMEDAC CONTAMINATION CHECK WITH NO SMOKE NOTED PER 21-00-01.