Uninterruptible power supplies (UPS) systems have to provide large amounts of power instantly after sitting dormant for months if not years, and this is a very different situation from traditional battery usage. This means new technology takes longer to implement. But the current shift is driven by the increased power density, providing smaller batteries or more power in the same UPS footprint, and the falling cost of lithium-ion (Li-ion) technology. But this shift in technology changes the sizing required for the batteries and the supporting electronics as Li-ion particularly is more prone to thermal runaway.

UPS systems range from a few Watts to power a PC for a few minutes, through mission critical systems supporting financial transaction servers, up to the world’s largest battery, 27MW of power in Fairbanks, Alaska, which has been running continuously for the last three years. But the technology is moving from the traditional lead acid, through nickel metal hydride to the same lithium ion cells used in laptop PCs.

French battery maker Saft is seeing its second generation Intensium1 Power Plus battery being adopted by three out of the top five telecoms operators for their UPS systems to keep 3G wireless basestations and IPTV running in the event of a power loss. Li ion is allowing twice the service life and higher temperature operation, says Saft. This battery system can deliver the same performance as a conventional lead acid UPS battery, but in a self-contained rack-mounted unit that is a quarter of the size and weight.

The Intensium 1 is aimed at short duration power backup in smaller, decentralised outdoor plant installations, required to support the new generation of telecoms networks, such as micro- and macro basestations and curbside equipment. It is especially suited for installations in hot countries where internal summer temperatures can reach 60°C – conditions where conventional valve regulated lead-acid (VRLA) batteries age rapidly, resulting in low reliability and premature failure and require complex monitoring systems. An anticipated 10 year life at 20°C is now 20 years, while at 40°C the life is extended from five to 10 years, and increase the maximum power from 3kW to 4 kW, providing headroom for the UPS designer.

Some of the first major telecoms applications for the Li-ion batteries include outside cabinets that support the IPTV service for one of the top three US telecoms operators, and micro-BTS deployment for UMTS service for the major European operator.

These base stations requires 48V or 24V batteries to provide up to 3.0kW of back-up power for a minimum of five minutes to ensure continuity of the GSM or UMTS services. In the case of failure of the main ac power supply this allows sufficient time for the BTS to either bridge to a reserve generator, or to bring its systems to a clean standby mode. The new BTS are outdoor installations containing up to six GSM or UMTS radios per cabinet.

As a result, Saft is upgrading its manufacturing plant in Poitiers, France, with dedicated assembly equipment in order to ramp up production to several thousand batteries per year.

But this does not mean Ni-Cd technology is out of the picture. Saft’s NCX Ni-Cd batteries have been chosen by AT&T in the US for the battery back-up service for parts of its wire-line network.

The NCX battery technology is specifically designed for telecoms networks that use a large number of remote network terminals. These terminals are typically without environmental control and several hundred thousand are today installed in suburban and small community locations in many parts of the world.

The NCX batteries are therefore optimised for long life under extreme temperature conditions and will survive without maintenance for up to 10 years. Ni-Cd is also at the heart of the $30m BESS (battery energy storage system) run by the Golden Valley Electrical Association in Fairbanks, Alaska. This provides a guaranteed 27MW for a minimum of 15min to stabilise the local power grid and holds the world record for the largest battery, delivering 46MW for 5mins during initial testing.

The previous (unofficial) world record holder was a 21MW BESS commissioned by PREPA (the Puerto Rico Power Authority) at Sabana Llana, Puerto Rico in 1994.

UPS systems are driving new standards in testing and monitoring batteries. New standards such as IEEE1184-2006, which was updated last year to include the testing and maintenance of Ni-CD batteries in standby systems, and a provisional standard PAR 1679, looking at the recommended practices for the characterisation and evaluation of emerging battery technologies in applications such as UPS.

This is particularly relevant for back-up cells that may have to sit for months or even years without being used and have to produce high current outputs quickly after long dormant periods.

The Valve Regulated Lead Acid (VRLA) battery systems have had significant potential problems with them, particularly with monitoring.

But companies such as BT have moved to VRLA throughout the company, and it has addressed the issue with a modular systems approach. But that does not work for all applications, and that has triggered a change in the standards that are used for testing batteries. This means the UPS system architecture is vital.

Remote electronic monitoring is seen as the way around the problem of sending an experienced engineer around many different sites to take measurements by hand, but there are issues that need to be addressed.

The vast majority of his business is installed on a UPS back-up battery system from financial and insurance companies to military and air traffic control systems.

The move to lithium ion also changes the battery monitoring regime.