Lithium-ion vs lead-acid (VRLA) UPS batteries: a buyer's comparison
Lithium-ion UPS batteries last longer, weigh less and recharge faster than lead-acid (VRLA), but cost more up front and are not a drop-in swap: lithium is chosen with the UPS. VRLA stays right for a UPS built for it, above all in mid-life. Lithium makes the most sense in a new UPS, in hot rooms and where outages are frequent.
Lithium-ion vs VRLA at a glance
| Lead-acid (VRLA) | Lithium-ion | Source | |
|---|---|---|---|
| Service life | 3 to 6 years | Upwards of 10 years (accelerated life testing); Vertiv quotes 8 to 10 years | Schneider WP 229; Vertiv |
| Weight for the same energy | Baseline | About three times less | Schneider WP 229 |
| Discharge cycles | Baseline | Up to ten times more, depending on chemistry, technology, temperature and depth of discharge | Schneider WP 229 |
| Self-discharge | Baseline | About four times less | Schneider WP 229 |
| Recharge | Baseline | Four or more times faster | Schneider WP 229 |
| Up-front cost for the same energy | Baseline | About 1.2 to 2 times more | Schneider WP 229 |
| Battery monitoring and management | Monitoring usually an add-on | Management built in, to control charging and discharging | Schneider WP 229 |
| Shipping rules | Regulated | Stricter | Schneider WP 229 |
Schneider's figures come from data-centre UPS work, and the exact gap depends on the lithium chemistry and how the pack is built; Vertiv's figures are from its article on lithium-ion for UPS. Schneider Electric White Paper 229 (2018) covers static (double-conversion or delta-conversion) UPS.
What Schneider's 10-year cost model found
White Paper 229 models a 1 MW three-phase UPS with 6 minutes of runtime at 25 °C. The VRLA batteries are refreshed in years 4 and 8; the lithium-ion batteries are not replaced. In that model, lithium-ion costs 82% more up front, 76% less to operate, and 39% less over 10 years, with a simple payback of 3.4 years.
Schneider names the factors that move the result most: VRLA service life, UPS service life, the price of each battery type, battery room area, VRLA maintenance and the cost of capital. Its example shows why: a VRLA life of 4 years with a UPS life of 8 years needs one battery refresh, and 2 more years of UPS life adds a second refresh. A small UPS under a desk is not a 1 MW system, so read the model for its logic, not its figures.
Lithium is a UPS decision, not a battery swap
Schneider is direct about it: lithium-ion batteries are not a drop-in replacement for VRLA. Even at the same nominal voltage, the UPS may need new firmware or hardware, because charging may change, the runtime formula may differ and the runtime estimate may be wrong, and the maker may need to integrate the battery management system with the UPS. Vertiv advises using only lithium-ion battery systems supported by the manufacturer of the UPS.
That is why lithium shows up in two forms in the catalogue:
- A lithium UPS, with the lithium battery built in, such as the Vertiv Liebert PSI5-1500RT120LI or the Vertiv Liebert Power-UPS Lithium PUL-400LVT.
- The maker's lithium cartridge for a lithium UPS model, such as the APC APCRBC170-LI cartridge for the SMTL1500RM2UC.
A UPS designed for VRLA takes a VRLA replacement, for example the APC Smart-UPS 600LS battery, the Tripp Lite Omni 600 LAN battery or the APC Back-UPS Pro 650 (BP650BLK) battery.
Retrofit, refresh or replace: it depends on the UPS's age
White Paper 229 assumes a data-centre UPS lasts about 10 to 15 years and sorts the decision by where the UPS is in its life:
- Under about 5 years old: moving to lithium-ion may make sense, because the lithium batteries will reach end of life at about the same time as the UPS, where the maker offers a lithium option for that model.
- About 5 to 10 years old: refreshing the VRLA batteries usually makes more sense; lithium may outlive the UPS by more than 5 years, though falling lithium prices can change that.
- Over about 10 years old: it may make sense to replace the whole UPS with a new one that uses lithium-ion, depending on what keeping the old one costs in service and parts.
Heat shortens both, but VRLA pays more often
Schneider's rule of thumb for both chemistries: battery service life halves for every 8 to 10 °C rise in average ambient temperature. Eaton's 9PX manual gives the figures for its batteries: a 3 to 5 year life, halved for each 10 °C above 25 °C, with replacement at least every 4 years. Because VRLA starts from a shorter life, a hot room means more frequent VRLA replacements within the life of the UPS, and Schneider calls lithium-ion much better suited to hotter rooms for that reason.
Lithium has its own limit. Schneider notes that lithium energy cells can rise about 30 °C internally while discharging; in a 40 °C room, that rise may make the battery management system shut the battery off to prevent damage. Sources: Schneider White Paper 229, Eaton 9PX user manual.
Safety
Vertiv describes lithium-ion UPS batteries as managed at three levels, cell, module and cabinet, and notes that the chemistries used in UPS, NMC, LFP and LMO, trade some energy density for longer life and are inherently safer than LCO, the chemistry of consumer devices. Vertiv also notes that IEC 62619 covers lithium cells for industrial use, including cell construction and the battery management system, but that no single standard yet covers the whole battery system. Schneider adds that UPS makers must pair the chemistry, cell packaging and battery management to each UPS: one more reason never to put lithium cells into a UPS built for VRLA. See Vertiv's lithium-ion safety paper.
When VRLA is still the right call
- The UPS was built for VRLA and its maker offers no lithium option for that model.
- The UPS is in mid-life, about 5 to 10 years old: refresh the VRLA batteries.
- The up-front budget decides: lithium-ion costs about 1.2 to 2 times more for the same energy.
When lithium-ion makes sense
- You are buying a new UPS and the maker offers it with lithium.
- The UPS is young and its maker supports lithium for that model.
- The room runs hot, where VRLA would need replacing more often.
- Outages are frequent: lithium recharges four or more times faster and tolerates many more cycles.
- Weight or space is tight: lithium weighs about three times less for the same energy.
Before you order: what to check
| Check | What to look for | Where to find it |
|---|---|---|
| UPS model number | The full model, not a look-alike | Front bezel, rear label or LCD menu |
| Battery chemistry the UPS supports | VRLA, or a lithium model or cartridge named by the maker | UPS manual or maker's product page |
| Battery cartridge or pack code | For example RBC or APCRBC codes | Old battery label, user manual or our product pages |
| Number of batteries, voltage and Ah | Every block in the set | Printed on the battery case |
| Connectors | Faston tabs, harness or keyed plug | The original pack |
For service on a UPS, see UPS battery replacement and repair and UPS maintenance services in Canada.
Frequently asked questions
Can I put a lithium battery in my lead-acid UPS?
No, unless the UPS maker offers a lithium battery for that exact model. Schneider states lithium-ion is not a drop-in replacement for VRLA: the UPS may need new firmware or hardware and an integrated battery management system.
How long do lithium UPS batteries last?
Schneider puts lithium-ion service life upwards of 10 years, from accelerated life testing, against 3 to 6 years for VRLA. Vertiv quotes 8 to 10 years.
Is lithium cheaper over the life of the UPS?
In Schneider's 1 MW model, lithium-ion cost 82% more up front but 39% less over 10 years, with the VRLA batteries replaced in years 4 and 8. The result depends on battery life, UPS life and prices.
Does heat affect lithium UPS batteries?
Yes. Schneider's rule of thumb halves service life for every 8 to 10 °C rise for both chemistries, but lithium's longer life means fewer replacements in a hot room.
Do you sell lithium UPS batteries?
Yes, as the maker's own parts, such as the APC APCRBC170-LI cartridge for the SMTL1500RM2UC, and as lithium UPS such as the Vertiv Liebert PSI5-1500RT120LI. Our replacement kits are sealed lead-acid (VRLA).