This is the time of year when a lot of people pull out solar-powered features that have been stored away for the winter. Outdoor solar lights, solar water features such as fountains and pumps, and solar powered bug killers and insect repellents are often only used when the weather is nice.

It also is the time of the year when outdoor solar lighting fixtures are found to not be working properly. And whenever a solar light or any solar powered product doesn't work, the usual fix is a new battery.

Solar lighting and most outdoor solar products generally use rechargeable batteries that last about two years, a pretty good life-span. Sooner or later though, replacements are inevitable. And that's where the trouble can start.

A mistake that many solar lighting users make is thinking that ANY battery will work with their solar light. Sorry, it's just not the case. Using the wrong battery may work initially, but within a very short time it will destroy the solar lighting fixture. This is true any product that uses rechargeable batteries, from relatively low-cost items such as flashlights to major investments such as laptop computers.

In fact, many specialists in battery technology recommend not only that the specified type of batteries be used, many suggest that the same brand of any battery be used in one specific electronic device.

Solar lighting fixtures are very particularly sensitive to the types of batteries used. Why? Because a well-designed solar light depends on the integration of three major components: the solar panel, the light used (usually LED but also halogen and CFLs); and the charging feature associated with the battery.

There are basically three types of rechargeable batteries used for outdoor solar products:

Nickel Cadmium (NICD, Ni-CD or Ni-CAD);
Nickel Metal Hydride (NIMH or NiMH); and
Lithium Ion (Li-ion or Li-Ion)

There are many technical differences between the three types cited above and this article does explore all of them. Instead, it explains some of the basic characteristics, advantages and disadvantages of the three types.

Rechargeable NiCD Batteries
Nickel cadmium batteries were one of the first types of rechargeable batteries used for solar lighting. In fact, if you want to determine when your solar light was designed (often an indicator of how current other solar components in fixture are), NiCD batteries often mean it is an older design. This doesn't necessarily mean it is an inferior product; it's just something to look at.

Advantages of NiCD
Ni-CD batteries are simple and fast to charge. Even if they have been stored for a while, an NI-CD the battery will usually take new charges well. They also are less sensitive to temperatures changes than other batteries, particularly Li-Ions.

NiCD batteries also are useful for items that need high discharge rates. (Put simply, discharge rate is the release of electrical supply from a battery to the item it charges.) NiCDs are cheapest rechargeable batteries to produce and usually the most inexpensive to buy.

Disadvantages of NiCD
As Ni-MH batteries and newer Li-Ion batteries came into favor, technology advances for NI-CD slowed down. Ni-CD batteries are not as powerful or as adaptable as other alternatives that were not cost-efficient just a few years ago.

Most important to many folks who use solar lighting because of its "environmentally friendly" nature, Ni-CD batteries are considered hazardous materials.

When Ni-CD batteries reach the end of their life-span, they must be disposed of as hazardous materials. Most municipalities have special collections or drop-off a few times a year when they will accept Ni-CD batteries and compact fluorescent lights (CFLs) along with other household hazards such as toxic paints or stains, certain cleaning products, etc.

Rechargeable NiMH or Ni-MH Batteries
Rechargeable Nickel Metal Hydride (NiMH) batteries are similar to their older NiCD counterparts, but generally considered to be a "better choice." They are commonly used in electronic devices because of their affordability, long life span and high charge rate. NiMH's are about twice as powerful as NiCD batteries and can be easily purchased in a variety of sizes. NiMH batteries are made with more affordable and less hazardous materials than NiCDs.

NIMH rechargeable batteryAdvantages of NiMH
Unlike NiCD, most specialists believe they are not impacted by "Memory Effect." Memory effect is complicated to explain and different people use it differently. In simplest terms, it means that for whatever reason a battery does not work as well as it could or should work.

Unlike NiCD batteries, they do not contain hazardous materials. And they are usually far less sensitive to temperature extremes than Li-Ion batteries.

NiMH batteries were specifically designed to provide strong performance in relatively high-drain electronic devices, such as solar lighting fixtures. They have a long life (about two years or up to 500 to 1,000 charge/discharge cycles. They are light weight and maintain strong power for about 80% of the chargeable cycle, for example one full day in the sun for solar products.

Disadvantages of NiMH
A main disadvantage of NiMH batteries is that they begin to lose their charging capacity when stored. An easy fix to this is to set a solar product using in the sun for two days before they are used at night, just as is recommended for new solar products.

The discharge rate of NIMH batteries is considerably higher than traditional lead batteries or more advanced Li-Ion batteries. (Discharge rate is defined as "the rate at which current is removed from a battery.")

Experts agree that considerable improvements have been made in NiMH batteries but limitations will remain. In fact, many view NiMH as an "interim step" towards lithium-ion technology.

Rechargeable Lithium-Ion Batteries
Lithium-Ion (Li-Ion) batteries are viewed as "state-of-the art" in battery technology. It's also expected that moving forward, Li-Ions will continually improve, gain more cache among electronic manufacturers, and be used more frequently.

The strongest form of batteries, Li-Ions are commonly used in consumer electronics. Li-ion batteries generally have a life-span of over 500 charge/recharge cycles.

They provide higher energy rates per weight. So, a Li-Ion battery of the same size and weight of a NiMH or NICD battery would produce twice as much power.

Advantages of Li-Ion
Li-Ion batteries do not contain hazardous materials such as lithium, cadmium, lead or mercury. At any given wattage, Li-Ion batteries weigh about half as much as NiCD or NiMH batteries of similar power. In general, they suffer from no "memory effect" and maintain their charge even when not used for long periods of time.

Disadvantages of Li-Ion
Because Li-Ion batteries continue to evolve, they are not considered to be a "fully mature" technology. In solar lighting and other products, special circuit protection must be incorporated into the design to maintain both voltage and currents within safe limits.

Many also believe that they "do not age" well, but this will improve as the technology evolves.

So, What is the Best Choice?
Overall, Li-Ion batteries are considered to be the best technology. However, being the "best" comes with a cost. Not only are Li-Ion batteries themselves more expensive than other alternatives, the technology required to effectively use them means a higher price tag.

Along with your budget, you have to consider what you want in terms of function and appearance. With a few exceptions, the best producers of solar technology do not always produce the widest selection or the most stylish products. It often takes a couple of years for the "best technology" to trickle down to other manufacturers.

As stated above, batteries are only one part of a solar light. The best battery will only work as well as the light, the solar panel and the way they all work together.

For solar lighting fixtures, or any other electronic products you now have, the battery specified by the manufacturer always is the best choice.

Otherwise, your batteries will just assault your electronic product.

Copyright 2011, SolarFlairLighting.com/AM McElroy