Narrative:

The propeller turned slowly during starting but did start. All systems were good; alternator was charging and all instruments worked properly. Aircraft lights; radios and other electrical equipment were turned on and in use. Upon takeoff clearance and during the takeoff roll; I noticed static in my headset and dimming of the instrument back lighting. Upon climb out at about 100 to 150 feet AGL; the lights and systems began to flash and then there was a total loss of electric power. I was moments from entering the cloud layer and still had the ground and tower in sight. I decided to make a hard 360 degree turn and returned to the runway I had just departed from. I had no radio contact with the tower and did not receive a landing clearance. I could see that there was no aircraft on final or in a 'line up and wait' position. Upon landing I taxied to the first available taxiway at which time the electric systems came back on line. In discussion with an experienced cessna retractable gear mechanic; I was informed that it was not that uncommon that when you have a low battery that the alternator will kick off when the gear pump is activated. This happens in take-off roll when the aircraft gets light and the 'squat' switch opens enabling the electric gear pump to build pressure for gear retraction. The pump being activated along with all the other electrical equipment puts a very big load on the alternator. The battery on the aircraft was inspected and found to have a dead cell. It was replaced and the aircraft was returned to service.

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Original NASA ASRS Text

Title: A C-172RG pilot returned to land immediately after takeoff because of an apparent loss of electrical which was later determined caused by a weak battery and the hydraulic pump starting at lift off in order to pressurize the landing gear retraction system.

Narrative: The propeller turned slowly during starting but did start. All systems were good; alternator was charging and all instruments worked properly. Aircraft lights; radios and other electrical equipment were turned on and in use. Upon takeoff clearance and during the takeoff roll; I noticed static in my headset and dimming of the instrument back lighting. Upon climb out at about 100 to 150 feet AGL; the lights and systems began to flash and then there was a total loss of electric power. I was moments from entering the cloud layer and still had the ground and Tower in sight. I decided to make a hard 360 degree turn and returned to the runway I had just departed from. I had no radio contact with the Tower and did not receive a landing clearance. I could see that there was no aircraft on final or in a 'line up and wait' position. Upon landing I taxied to the first available taxiway at which time the electric systems came back on line. In discussion with an experienced Cessna retractable gear mechanic; I was informed that it was not that uncommon that when you have a low battery that the alternator will kick off when the gear pump is activated. This happens in take-off roll when the aircraft gets light and the 'squat' switch opens enabling the electric gear pump to build pressure for gear retraction. The pump being activated along with all the other electrical equipment puts a very big load on the alternator. The battery on the aircraft was inspected and found to have a dead cell. It was replaced and the aircraft was returned to service.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.