A traditional sealed lead-acid battery pack is typically designed for a three-minute discharge event. However, most data center providers prefer battery packs that deliver five minutes of continuous standby power, providing the margin of safety they need for copying large data sets from cache memory to nonvolatile memory in the event of a power failure.

Creating a LiFePO4 battery pack assembly is actually quite achievable for qualified design teams. LiFePO4 is an energy dense type of battery that offers a high discharge rate, superior safety and long cycle life. LiFePO4s have a charge voltage three times greater than a NiCd cell and nearly 10 times the energy density of comparable sealed lead-acid batteries.

The lead-acid batteries in traditional battery packs are sealed, but not maintenance free. They must be routinely monitored using voltage checks, load tests and physical inspection. All common 18650 battery technologies are subject to sulfation, in which small sulfate crystals form on the battery plates if stored for long periods without recharging. However, LiFePO4 batteries are better able to resist sulfation under partial-charge conditions. 

The phosphates component of the LiFePO4 cathode also means the battery can handle high temperatures as well as overcharge and short-circuit conditions quite well. The cells are unlikely to experience thermal runaway and the memory effect  that affects some other technologies. LiFePO4s also do not require scheduled cycling to prolong service life. As long as the electronic drain is low, they can maintain a minimum state of charge for up to one year with no external power.

LiFePO4-powered BBUs can greatly improve stand-by power capabilities, but creating LiFePO4 battery packs that are safe and reliable requires skill, specialized knowledge and experience. While the cells are extremely safe, assembling multiple cells into a pack with sufficient power and runtime to operate a server requires careful design to deliver optimal performance. All battery packs, but especially LiFePO4 battery packs, need to be part of a properly designed system or they may rupture, ignite or explode when exposed to high temperatures, drops or other abuse.

However, design engineers can develop battery packs that include specific types of protection devices such as integrated circuits  for controlling NiMh battery cell voltage. Safeguards are essential for preventing surges or sags in voltage that could damage downstream devices and the battery pack itself. An effective design also includes a thermistor that measures temperature and shuts down the pack if the temperature increases beyond a predetermined maximum.