Battery Technology for Data Centers: VRLA vs. Li-ion

Overview

The paper compares VRLA and Li-ion batteries in three-phase UPS applications on energy density, life, footprint, weight and temperature sensitivity. It then runs a 10-year total cost of ownership (TCO) for a 1 MW UPS with 6 minutes of runtime. Li-ion costs more up front but needs fewer replacements, less space and less cooling. This comparison shows that battery choice must be judged on space, cooling and replacement cost together, and not on battery price alone.

The results are concrete: Li-ion TCO over 10 years is 39% lower than VRLA. In the 1 MW case, battery capex is about 82% higher for Li-ion ($132k versus $73k). Service life at 25°C is 4 years for VRLA (range 3-6) and 12 years for Li-ion, while calendar life is 5 versus 17 years. Footprint is 5.4 m² versus 2.2 m², and weight is 11,340 kg versus 2,767 kg.

Temperature has its own section: battery life halves for every 8-10°C rise in average ambient temperature, which is why battery rooms should be held near 25°C. End of life is defined as 80% of rated capacity. In the model, trickle-charge losses are 0.2% of UPS load for VRLA and 0.1% for Li-ion. A sensitivity analysis identifies the main TCO drivers. A limit is that the results rest on a specific 1 MW / 6-minute case and the model's cost assumptions, so ratios may shift at other capacities and prices. Even so, the paper gives a basis for judging battery chemistry on lifecycle cost rather than purchase price alone.

Key points

1. 10-year TCO for a 1 MW UPS: Li-ion is 39% lower than VRLA.
2. Battery capex is about 82% higher for Li-ion in the 1 MW case ($132k vs $73k); generally 1.2-2x for the same energy.
3. Service life at 25°C: VRLA 4 years (3-6), Li-ion 12 years; calendar life 5 vs 17 years.
4. Footprint 5.4 m² vs 2.2 m²; weight 11,340 kg vs 2,767 kg for 1 MW / 6 min.
5. Li-ion is about 3x lighter for the same energy and offers up to 10x more cycles.
6. Battery life halves for every 8-10°C rise in average ambient temperature.
7. End of life is defined as 80% of rated capacity.
8. Trickle-charge losses: VRLA 0.2%, Li-ion 0.1% of UPS load.

Using it in design

• Add battery catalogue parameters: chemistry, service life at 25°C, m² per kWh, kg per kWh and floor loading.
• In the runtime calculator, derate life by 50% per +8°C above 25°C and size for end of life at 80% capacity.
• In the TCO module, calculate replacement cycles over the UPS life (10-15 years).
• Run a floor-loading check for VRLA rooms.

Who should read it

Designers selecting UPS and battery technology, and those making the investment decision.

Related standards

• IEC 62040-1
• IEEE 1184
• IEEE 485
• UL 9540A
• NFPA 855

Publication details

Authors

Victor Avelar; Martin Zacho

Publisher

Schneider Electric

Year

2018

Document number

WP 229

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation