Standby Power Batteries Guide

Batteries provide a source of standby DC power from a chemical reaction. Within a power protection plan sealed lead acid (SLA) batteries are used in uninterruptible power supplies and dc standby power systems. A battery is also a critical component within a generator starter motor circuit. Within renewable power applications batteries are used for energy storage; conserving the energy derived from solar and wind power systems for later usage. See the EcoPowerSupplies range of replacement UPS batteries.

Battery Construction

A single battery is referred to as battery block. Its case is typically made from polypropylene PVC (which can be flame retardant to UL94V-0), and has individual positive and negative terminals. The electrolyte within the battery is typically Sulphuric Acid and this liquid (or gel) fills the space between the positive and negative plates, forming a closed circuit of individual cells with an electrical potential for later discharge.

Battery Sizes

Battery sizes are referred to in ampere-hours (Ah) and cell number per block: 2Vdc, 6Vdc or 12Vdc for example stands for 2, 6 and 12 cells. The Ah rating refers to the amps the battery block can deliver per hour. The term ‘battery set’ refers to a number of batteries arranged in series, into a connected string or number of strings. The Vdc of the battery set must be equal to the input Vdc of the device to be powered – a UPS inverter, solar inverter or DC power standby system. For example a 48Vdc input would require a 48Vdc battery set comprising of 4 sets of 12Vdc battery strings or 8 strings of 6Vdc batteries.

The battery set used within a standby power application is sized to provide a specific runtime (minutes or hours) at a specific Real Power load (Watts, kW or MW). Battery manufacturers size battery sets based on these and a number of other system specifications including the operational ambient of the room and end-of-life state required. For example, some specifications call for an 80% capacity at end of working life.

Battery Design Life

Batteries are a consumable item and age through use and general chemical interaction. The typical design life for batteries within an uninterruptible power supply or DC standby power system is 5 years at 20-25˚C or 250 charge/discharge cycles. This means replacement of the UPS batteries will typically happen between years 3-4. Ten year design life batteries will see replacement normally within years 7-8. Ambient environment is one of the biggest factors affecting operational working life and overall performance. Battery life reduces as temperature rises (and can half above 30˚C) resulting in an actual increase in performance (runtime) which is temporary.

Sealed Lead Acid Maintenance Free Batteries

Lead acid is the most common type of plate-electrolyte with others including: Nickel-Cadmium, Lithium Ion or Silver Alkaline. Lead acid batteries are available in industrial, automotive and traction design types with design lives of 5, 10 and 15 years.

UPS systems use industrial valve-regulated sealed lead acid (VRLA) batteries due to their charge/discharge performance and operational characteristics. This makes the UPS batteries more suited suited to office, datacenter and domestic environments. Their sealed, compact size, low gas emissions and design (which allows horizontal or vertical installation) makes then ideal for use within compartments, cabinets and racks. VRLA batteries can be installed either horizontally or vertically as their pressure valves only open when required to do so in extreme circumstances.

Absorbed Glass Mat (AGM) VRLA type are the most commonly used for standby power applications including UPS systems, security and fire alarm panels, telecoms, emergency lighting, DC standby power systems and renewable energy storage devices. Another type of VRLA battery is the Gel filled type. In comparison, generators use automatic batteries, which are more suitable for driving a starter-motor.

For larger kVA/MVA-rated applications, open-vented (wet-flooded) batteries may be used. These are not suitable for confined spaces as they gas when full charging is applied. Open-vented batteries are typically installed in a battery room, which is secure and isolated, with appropriate wash-down facilities, splash mats and bunded containers in case of acid spills when electrolyte is topped up or battery blocks leak. Open-vented batteries are most commonly installed on racks within such environments for ease of access and may be installed with individual battery block status monitoring.

Renewable Batteries

OpzS and OPzV are battery types with tubular plates. They are designed for industrial and renewable power applications including solar and wind turbine energy storage. The tubular design typically has a lead selenium alloy which help to guarantee a long operating life with minimal maintenance and optimal cyclic performance. OpzS and OPzV may be suitable for use as solar batteries and other renewable applications including wind turbines for energy storage.

Lithium Ion Batteries

Lithium-ion batteries are another type of rechargeable battery. Typically found within consumer electronics due to their energy densities, lack of memory and slow loss of charge when not in use. Lithium-ion batteries are becoming more popular in military, electrical vehicle, aerospace and energy storage applications as battery manufacturers extend their Ah-rating.

Li-ion batteries require a more sophisticated battery management system than lead-acid.

Supercapacitors (Ultracapacitors)

Supercapacitors store electrical charge. In some applications their high power density makes supercaps a viable alternative DC power source to a traditional sealed lead acid battery set. Some UPS can be configured to work with supercapacitors, especially where only a short runtime is required. The advantages of supercaps over traditional batteries include:power density, recyclability, lightweight, safe and eco-friendly characteristics, in addition to being able to operate at high ambient temperatures without degradation in runtime or working life.

and can be found in some UPS applications, where they provide a replacement source of DC power to a traditional battery set. Supercapacitors are more tolerant of temperature extremes and


Batteries will age and discharge even when not connected to any other battery or electrical system. The typical storage life for a battery is approximately 6-12 months, taking into account the ambient temperature and internal discharge rate. Batteries and products using internal batteries therefore require recharge at the end of this period to avoid unnecessary deep-discharge states beyond which they may not be rechargeable.

Replacement Batteries

When selecting UPS replacement batteries or batteries to replace those used within other standby power applications, batteries with equivalent Ah and Vdc ratings must be used. In addition:

  • Wiring and Terminations: care must be taken to ensure the terminal connection points match so that existing wiring terminal connectors can be used.
  • Battery Ageing: when replacing batteries that have failed or are weakening, it is important to replace an entire battery string and/or battery set. This is because the performance of the newly installed batteries can quickly degrade to the level of the weakest existing battery.

Batteries can be monitored and tested for performance either through internal battery testing routines or external impedance testing. Visual inspections can also help to identify ageing batteries. Plastic cases can buckle and white deposits show around terminals as batteries are subjected to charge/discharge cycles and general ageing.

If ordering replacement UPS batteries remember to specify if the links are to be included with the shipment.

Battery Recycling and Disposal

Batteries are classed as hazardous waste and must be transported, disposed off and recycled according to national guidelines. In the UK, the application Acts and Regulations include: the Environmental Protection Act 1990 and Hazardous Waste Regulations 2005 apply with additional applicable European directives including:

  • Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC
  • EU End-of-Life (ELV’s) Directive (September 2000)
  • EU Batteries Directive (May 2006)

Please call us on 0800 612 7388, complete an enquiry form form or email us for more information on the EcoPowerSupplies range of batteries.