Technical article on the decisions needing to be considered when choosing which battery chemistry when specifying your UPS system by Warren Venn
An essential element of any UPS system is the battery, however the different chemistries available cloud end user choice.
As the UPS is designed to be always on to provide the reliable power source for critical systems, it’s therefore essential that the battery can provide a reliable power source and be easy to discharge and recharge effectively.
Major points to consider regarding the battery are safety, reliability and cost of ownership. The factors affecting all these are the different battery chemistries that are available, some of which are more suitable for different applications.
In this article we will discuss these different chemistries, their pros and cons and look at a newer technology that might be coming soon.
Standard UPS systems were originally built using Valve-Regulated Lead-Acid (VRLA) more recently Lithium Ion (Li-Ion) has become prevalent especially for systems where cost is not a driving factor or where the environment is harsh.
We will discuss each of these and their pros and cons.
Valve-Regulated Lead-Acid (VRLA)
- Description: Sealed lead–acid, maintenance-free
- Pros:
- Low upfront cost
- mature known technology.
- Cons:
- Heavy and bulky
- limited cycle life (300–500 cycles)
- requires limited depth-of-discharge (DoD) to extend life
- moderate efficiency (~70–90% round-trip.
- Costs:
- Cheapest upfront, but frequent replacements increase total cost of ownership
Lithium-Ion (Li-ion)
- Description: Chemistry optimized for energy, safety, lifetime .
- Pros:
- High energy density (150–250 Wh/kg vs 30–50 for VRLA);
- deep DoD (80%+), long cycle life (1,000–5,000+ cycles);
- high round-trip efficiency (85–95%)
- compact; low maintenance; fast recharge; long calendar life (10–15+ years)
- Cons:
- Higher upfront cost (1.75–2.3× VRLA for small UPS)
- safety depends on chemistry and Battery management System;
- extreme-temp performance considerations.
- Costs:
- Li‑ion total cost of ownership becomes superior in around 5 years;
- 40% lower over 10 years for single-phase UPS.
Nickel–Zinc (NiZn)
- Description: Emerging chemistry for UPS, especially data centers.
- Pros:
- Higher energy/power density than VRLA
- non-flammable; wide operating temperature; long life (3× VRLA)
- reduced footprint and cooling needs.
- Cons:
- Less common, limited availability; technology is still very new.
Technical Comparison of Battery Chemistries
Cost Considerations & Total Cost of Ownership
- Upfront cost:
- VRLA lowest.
- Li‑ion (small UPS) 1.75–2.3× basic VRLA
- NiZn is still emerging, and initial costs are higher.
- Total cost of ownership (over typical UPS life):
- Li‑ion often around 2.8× cheaper per usable kWh; up to 40–50% savings over 10 years
- VRLA costs are driven up by replacements taking into consideration labour and disposal costs.
Application Suitability
For Small/Office UPS:
VRLA remains cost‑effective for infrequent or light-duty backup.
For Data centres , edge computing and remote facilities:
Li‑ion is ideal, its energy‑dense, compact, low‑maintenance, Total cost of ownership
Mission-critical/infrastructure:
Li‑ion is best choice, offers temperature stability and long life.
So Which Chemistry is best fit for my application?
So in conclusion when choosing a UPS battery chemistry, please consider initial cost vs lifecycle cost, size/weight constraints, maintenance demands, the operating environment, and desired reliability. In short VRLA remains viable for low-cost, low-duty needs. Lithium-Ion currently leads for long-life, high-density, mission-critical roles.
A version of this article originally appeared in CIE July/August 2025 issue.
