I installed several solar powered LED lawn lamps…these were made by a firm called “Malibu” (made in China), The lamps are connected to a charging module that has a solar cell with three NiMi H rechargeable batteries-only one works now. My question: assuming the interior circuitry is still good, how longs should these things last? The plastic resin over the solar cells is all clouded and yellowed-so is it a case of just throw away and replace?
I’ve got some that are very old, that sound just like yours. I stuck new Ni-Cads in from Harbour Freight and they worked again, for a while. The batteries that came with them were better, but they do eventually die. But the solar thingy seems to still work.
So, I guess if replacing the batteries is cheaper than replacement of the whole thing, than a hearty “Maybe!” 
Replacing the batteries has improved mine quite a bit. The variance based on the light is usually less than the variance caused by the amount of sunlight we get during the day. Batteries first, then if they don’t stay on long enough, replace it. Mine are cheap, though. I just replaced one yesterday, because some clown ran it over and took it.