Batteries for Your Solar LED Light
Batteries 101
Our solar LED lighting products use NiCad battery packs because for overall performance they provide the best solution for storable power.
NiCads have an observable memory effect (meaning they will tend to only charge a certain amount based on what they are used to). However, this has ONLY been observed in situations where the battery has been discharged to the exact same level for numerous cycles (>50). NASA experienced memory effect in its early satellites that orbited the earth for several months, when they tried to charge the batteries to a greater charge (fuller), the batteries where not able to take this charge. The solution was to drain the batteries below the level that they had been repeatedly drained to, then they where able to receive a greater charge.
In the case of the Sollight's solar powered LED lights, it is unlikely that the batteries will receive either the exact same charge or discharge for more than 50 cycles, so the memory effect should not be a problem.
However, NiCad batteries do lose (discharge) 1-2% per day while inactive. This also depends on the level of charge (faster when full), and temperature (faster when hot)). So even if the batteries are fully charged, they will essentially be dead in 90 days. We recommend that you keep your Sollight products fully charged whenever possible, and that you give it a good direct sunlight charge at least once a month if you keep it stored.
Finally, while there are several other types of battery/charging systems available, NiCad batteries have the best shelf life of the declarable battery family. NiMh batteries, often used in items that will receive a daily recharge (cell phones, laptop computers, VHF radios, etc.), discharge at a rate of 3-4% a day.
Charging 101
There are two basic types of solar panels (also referred to as a PV - photo voltaic cell): mono-crystalline and poly-crystalline. Each has it's own output characteristics.
Our Siemans solar panel is made from Polycrystalline silicone. It yields a slightly higher charging output than a mono-crystalline in direct sunlight, slightly less in overcast conditions.
Our panel is rated at 60mA, meaning it will put out 60 milli-ampers of power each hour. In direct sun we have tested our panels up to 72mA; in overcast conditions they may go as low as 6mA.
Why is this important? Our NiCad batteries each hold 700mA of power; we use two of these, for a total capacity of 1,400mA. Thus, if the PV is putting out an average or 50mA per hour, it will take approximately 28 hours to fully charge the batteries. This, in turn, should power the WHITE LED for around 20 hours. As the batteries discharge, the output voltage will also decline slightly, along with the brightness of the light.
For this reason it's always good to keep the batteries charged, and to keep the PV exposed to light whenever possible (to top off the batteries). Even a few hours in a well lit room can add a half-hour of burn time to your Sollight products.
