FAQs - UPS Batteries

A Valve-Regulated Lead-Acid (VRLA) battery is a type of battery used within a applications that require a back-up or standby power source. Examples include uninterruptible power supplies, emergency lighting systems, security panels and generators (for the starter motor).

The term ‘battery block’ refers to a complete individual battery. Multiple battery blocks can be connected into a battery string. A battery cell is an electrical circuit within an individual battery block consisting of positive and negative electrodes or plates, an electrolyte and separator. The battery cell will have a Vdc and will be arrange to make up the overall Vdc of the battery block. For example a 12Vdc battery block may comprise of 12×1Vdc battery cells.

Lead acid batteries are typically designed for either 5 years or 10 years. This is known as their design life. Battery life is also dependent upon a number of other factors including ambient temperature, charging technique and the number of charge/discharge cycles. A typical 5-year design life battery will require replacement around years 3-4 of operation and a 10-year design life battery around years 7-8.

The F1 and F2 terms refer to the push-on terminal size. F1 terminals are 0.187inches wide and F2 terminals are 0.250inches wide. Typical applications for F1 sized battery terminals include standby power emergency lighting and for F2 size terminals the most common application is emergency power backup including DC power supplies and uninterruptible power supplies.

Some batteries are sized in Watts and others in Ampere-hours (Ah). To convert Watts to Ah divide the Watt figure stated for the battery by the dc voltage of the battery. For example a 360W 12Vdc battery is a 30Ah battery.

A UPS system is designed to bridge breaks in the incoming mains power supply for a set duration. This can be for a brief period, to power through momentary outages lasting milliseconds to a few minutes, or for longer durations, sometimes up to several hours. Most UPS systems provide 5-30 minutes of runtime. Available runtime depends on the load (kVA/kW) the UPS is powering, the battery charge percentage, and even the battery’s age. The most commonly used battery is a valve-regulated lead-acid (VRLA) type, but some UPS can also be installed with lithium batteries. For long-duration runtimes, a UPS system is installed with one or more battery extension packs, providing runtimes lasting hours, supported by a smaller battery and a local standby power generator.

Most UPS batteries, whether valve-regulated lead-acid (VRLA) or lithium-ion, should be visually inspected and load-tested at least once a year to ensure they can deliver their rated runtime during a power outage. For smaller UPS, this can be done by disconnecting the mains power supply and using the connected load. For larger systems, with an external UPS maintenance bypass, the same process can be used but with a load bank to simulate a load on the UPS. Most UPS systems will automatically test every 24 hours, and it is important that UPS are connected to remote monitoring systems to ensure alarm conditions are picked up, and corrective action can be taken. For larger UPS systems with batteries on external stands, visually inspect UPS batteries at least monthly, and you may also need a complete battery monitoring system.

Most UPS batteries are VRLA up to 10kVA. VRLA batteries are available with two design lives: 5 years and 10years. It is not uncommon to replace 5year design life VRLA batteries in years 3-4 and 10-year in years 7-8. Lead-acid batteries degrade over time, and the rate of degradation depends on usage and ambient room temperature, which should ideally be within 20–25°C if the design life is not to halve. Lithium-ion batteries are less sensitive to heat and have design lives in the 10-15year range.

A UPS system provides instant battery backup to keep critical connected loads running. Battery runtime (or duration) is typically 5-30 minutes, which is suitable for most applications. Where a longer runtime is required, the uninterruptible power supply is installed with a larger battery set, usually an externally connected battery extension pack or a standby power generator.

As generators can take up to 1-2 minutes to come up to full cycle power after a cold start, the UPS battery covers this period, preventing the connected loads from a power outage and a break in electrical supply. Once up to and stable, the UPS input then synchronises to the generator supply and reverts to battery charging. The process is seamless to the connected loads, as the UPS inverter constantly powers them. When the mains power supply returns and is stable, the UPS system synchronises its input to the mains, and the generator powers down. An Auto Mains Failure (AMF) panel monitors and controls generator start-up and power-down.