My mom loves the solar LED lights and has them in the front and back yard. I notice some of them last longer than others. Some she bought probably 8 years ago there are one or two still working with new batteries but others don't last but about one or two years. The older ones have an orange bulb that looks like HPS color light. Most of the others have a white light to them. I kind of like some of them, my favorites are the lanterns that hang on little hooks and also the ones that look like post top lanterns. I have seen some others that mount on gutters that have 3 LEDs in them. The plastic ones tend to get brittle though from the sunlight.

For solar lights, I always check the batteries and the circuit board to make sure its functioning correctly or not.

Most common problems Ive seen:
- Too small cell to handle the overcharging at high temperatures. Many modern lanterns use AAA or sometimes a small button cell, which do have sufficient capacity to operate the LED, but way insufficient to handle the overcharging at hot evening. The solar panels, although very small, can deliver about 50..80mA when on full sun. That needs at least AA size cell to handle that current. Rated capacity should be of abou 600..900mAh (but still in an AA format), not higher. the thing is, the cell has to have enough of both internal room to handle the gasses when overcharging, as wellas the water recuperation electrode reserve (one electrode is designed with significantly higher capacity than the other, this extra then eats awya the generated hydrogen and oxygenduring overcharging). Theconsequence of these margins is, you can not fit more than the 900mAh into an AA size canister.

- Other aging problem is corroded plastic covering the solar cells. The UV exposure makes the material rather opaque and so the cells loose power.

- And yet other problem is water andmeral corrosion. Whatever looks as "pervectly sealed" will most likely suffer the most. The problem is the changing temperature between day andnight, which forms rather high pressure difference between the "sealed" compartment and outer air, the seal most likely wont be able to hold that long, so the water may seep in (rain after a hot day is the worst, but just the night condensation is sufficient). Andbecause the thing is designed as sealed, the water will not get out, it will stay there even for the next hot days and aided by the high temperature do all the metal corrosion business...
So to preven these problems, always look for light, which do have decent "roof" to cover from the rain, but otherwise are well open and ventilated, so the humidity is not able to collect there. The ventilation helps the battery too - the moving air does reduce the temperatures inside a bit. Dont forget 10degC lower temperature uses to mean double life with many aging mechanisms...

with the development of LED, nowadays, solar street lights become more compact, they can integrate light source, panel and battery into one unite,
and this facilitates the solar lighting industry. in my experience, the weakest parts of solar lights are its controller and batteries,
more failure caused by the solar charge controller.

here is a definitive introduction guide of the solar charge controller, hope this can be helpful
https://enkonn-solar.com/solar-charge-controller/

with the development of LED, nowadays, solar street lights become more compact, they can integrate light source, panel and battery into one unite,
and this facilitates the solar lighting industry. in my experience, the weakest parts of solar lights are its controller and batteries,
more failure caused by the solar charge controller.

here is a definitive introduction guide of the solar charge controller, hope this can be helpful
https://enkonn-solar.com/solar-charge-controller/

That is, what you need for lead acid batteries. It makes the system more complex, so it makes sense for higher power units (like the streetlights,...).
For small garden lights using proper overcharge tolerant cells is the easiest way to go (hypothetically that would work for the larger streetlight as well, but the battery cost and waste heat management would make it way too expensive and even complex, so it is better to use the controller there).

There are few technical mistakes in the text (however the recommendation on how to use the system seems to be correct):
- The discharge does not form sulfate crystals, but the PbS is in an amorphous form. It is when the amorphous material crystallize, the battery capacity get lost (amorphous PbS get dissolved by charging, but the crystals do not anymore)
- The "equalizing" (as described) is not that much about equalizing one cell towards others (like in e.g. LiIon cells; that happens during the float charge), but "equalizing" the content across the cell internal volume, the hydrogen bubbles are intentionally generated (for some short time, after some period of time, like 30 minutes every month or so) to stir the cell content. In cars the same is done by the car movement, therefore the battery should be placed with cell plates longitudinally, so car acceleration and deceleration is able to stir the electrolyte. Well, many car makers do follow that, but many place the battery where was the last place in the engine bay, often sacrificing the possible battery life (it survives the car warranty either way, so many don't care).
This stirring is possible and needed only with flooded cells, where the electrolyte mix may get separated by gravity and where the bubbles are able to mix it back. With gel or similar electrolyte forms this should not be done (by the overcharging), as it always means some water loss, but because the electrolyte is rather immobilized by the gel, it is not needed either.