As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
HAD A BURNING SMELL IN THE AIRPLANE AND FOUND SMOKE COMING FROM THE BATTERY AND BATTERY CHARGER. REMOVED AND REPLACED BATTERY AND CHARGER. THE 737-291 AIRCRAFT HAVE A PROJECT TO INSTALL NEW CELLS. THE OLD CELLS HAVE BEEN FOUND TO OCCASIONALLY OVERHEAT BECAUSE OF POOR SEPARATOR MATERIAL BETWEEN CELLS. OPS CHECK GOOD.