From Alkaline to Zinc, there are many types of batteries. Some have practical application. Some are only experimental. All are used as a means to store electricity.

Since the beginning of the Space Program and, now, with development of electric cars and solar power, battery technology has evolved in general and in certain specialized applications.

SEALED LEAD ACID

Most UPSs in support of computers and other digital processing equipment rely on lead acid batteries. Those use the same technology as the battery in a gasoline powered car. Invented in 1859, the lead acid battery is reliable and inexpensive. Unfortunately, it is heavy and large for the amount of power it  can produce compared to several other battery types. Some lead acid batteries require maintenance to keep liquid electrolyte levels up. Batteries in UPSs do not require maintenance.

LITHIUM IRON

Recent rapid growth in the use of lithium iron batteries began in 1991 when Sony commercialized that technology.  By many comparisons to advancing technology, this is a well developed and mature battery design. Lithium iron is a low maintenance, high energy density type of battery technology. Most of today's mobile phones run on a single LiFe cell.

The most economical lithium iron battery in terms of cost-to-energy ratio is the cylindrical 18650 (used in the Juice Goose SL-350 UPS). The name derives from its dimension,18mm x 65mm (0.7" x 2.5"). Picture a larger AA battery. This is a very adaptable and reliable battery design. It's a truly amazing fact that the Tesla "battery" is made from strings and bricks and layers of over 6,800 of these individual 18650 cells. 

Like all battery technologies lithium iron batteries call for proper application and management. They require a protection circuit to limit the peak voltage during charge and to control voltage and current on discharge. In addition, the cell temperature should be managed to avoid extremes. Storage and/or use in a temperature controlled environment will increase the life of the battery.  But, LiFe battery technology certainly provides a small, economical and powerful alternative to lead acid and other existing options.