The potential danger of total battery failure in the 737-300.

[Centaurus]

Many years ago in a New Zealand 737-200 when the cargo hold door was opened after engine shut-down smoke was seen coming from that area or it might have been the E&E Bay, I don't remember. Investigation revealed a battery defect. It was not known when the battery defect occurred. A Notice to Pilots was issued requiring crews to monitor the battery voltage during APU start and if the voltage was less than 15 volts at any time during the APU start cycle the battery was defective and rectification action taken before the aircraft flew. The technical reason given was that the APU start requires battery power and it is only then that the true condition of the battery is checked.

Fast forward to the January 2002 accident to a Garuda Indonesia B737-300 that flew into a 63,000 ft thunderstorm causing both engines to flame out on descent. Relight was unsuccessful as the aircraft was still in heavy rain. The crew tried to start the APU but then a total electrical failure occurred leaving the crew with loss of both engines and loss of all electrical power in IMC.

The aircraft broke out of cloud at 8000 ft and ditched flapless into a shallow river with only one fatality. Later investigation revealed that one of the cells of the battery had been found to have a lower electrolyte level to the point causing insufficient current storage. It caused a high resistence and resulted in the battery voltage drop which accounted for the reported failure of the battery. The loss of the battery liquid was due to a spewing effect (i.e. convective movement of electrolyte out of the cell).

The spewing was caused by high temperature and over-charging. The reason why the high temperature and over-charging could occur was the absence of the high temperature sensor on the battery the function of which is to stop charging when the battery temperature is too high. The detchment of the temperature sensor was due to corrosion of the sensor mounting.

An interview with the pilot revealed that the battery was at 22 volts when re-start was initiated. This fact was used to develop a battery test. The test revealed the battery will run out of power before the APU start sequence could be completed it it indicates less than 22 volts at the beginning of the procedure. From wreckage examination it was found the APU inlet door and the APU fuel shut-off valve were still in the closed position. This indicated the APU start process failed at the initial stage. It was concluded that the battery had already run out of power at the initial stage of the APU start. Following this event the ignition system may also fail because the electrical power remaining was insufficient.

Question: The B737 FCOM does not require the crew to monitor the battery volts drop that will occur at the instant of the APU start cycle. This despite the fact that max load will be on the battery at the instant of APU start. In other words, the only time the crew can check on the true health of the battery is at the start of the APU start cycle. if that statement is correct then I wonder why Boeing do not mention the fact. It seems a good precaution to me. Are there alternative crew methods of checking the true health of the battery in-flight or on the ground?