I would say that 80% of the Alpan/Siemens Malibu solar lamp problems are due to batteries. Also Malibu and Brinkmann, etc. The remainder of problems are due to incandescent bulbs or bad electrical connections or failed components on the control circuit board. Least suspect are the fluorescent lamps, which have a very long life and usually can be ignored. 

Batteries: Measure with a digital multimeter. An analog meter is often not accurate enuf. For two batts in series: 1.5 V is too low. 1.8 is minimum to operate. Most Alpan/Siemans lamps shut off when batt voltage is low. Expect 3 years batt life. More life as you go further toward equator. Shorter life as you go North. (There is a remedy for short batt life: double-up or triple the batt pack so that it is not so severely drained on each discharge cycle). Also, one should shut off the lamps for 2-4 days, several times a year; so that they get a deep charge. Remember, NiCad batts that are used in the small yard lamps have a very long shelf life. They are not damaged by storage in discharged state. The opposite is true for the lead/acid batteries used in SensorLights: these are damaged by storage in the discharged state. Lead acid batteries love to be maintained at full charge. To store a SensorLight indoors, leave the solar panel facing a window with switch OFF.
Circuitry: To test the units, substitute a fresh batt pack for the existing one. We also test them on the bench using a DC power supply of 2.4V for the units using two batts in series or 3.6V for three batts in series. Then turn out room lights to see if lamp turns on.
If, after replacing batts,  the unit works but again fails to come on after about a week, then the batts are not being charged by solar. Look for bad connections to the solar panel. Substitute another solar panel from a good unit to verify. Still doesnt charge? Circuit board is faulty.
Fluorescent Bulbs: The fluorescent lamps operate at about 400V AC, at a high frequency. Too high for an ordinary AC voltmeter. So we use an oscilloscope or RF-type AC voltmeter to verify that the AC is present. If AC is OK but lamp is out, then you probably need a new fl tube. Or clean the exterior of the tube in case dirt is forming a shorting path. If AC is not present (with room darkened), but DC input is OK, then the electronics board is faulty. Note: if using an oscilloscope, note that the lamp is a high impedance, balanced load. Most accurate reading will be obtained using a balanced scope input.

Replacement Parts: Batteries and bulbs are available. ALso, major parts shown in the above diagrams are available. Beyond that you are on your own. Hint: For some customers we have taken parts from several of their old lamps to make one good lamp. - - Al

LAMP LOVERS: Let me know if you ever find a more detailed Alpan/Siemens information
site. With their permission I will add that info to Al's. And I continue to recommend that you keep those 1-Watt lamps working: there is nothing brighter, new on the market. - - John