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Lithium-ion battery FAQ

Lithium-ion UPSs represent a significant progression in UPS battery technology, which for decades has been dominated by valve-regulated lead acid (VRLA). Because lithium-ion batteries offer a 10- to 15-year lifespan—as opposed to their lead acid counterparts, which generally need to be replaced every 3 to 4 years—the technology offers a number of advantages. 

What are the primary benefits of switching to lithium-ion UPS batteries?

The most common reason cited is the significantly longer service life. Lithium-ion also provides a greater cycle life (the number of charge/discharge cycles ranges from 5000 to 9000, versus approximately 500 for VRLA batteries), as well as a longer warranty. Furthermore, the lighter weight and smaller footprint are additional benefits.

In addition, IT professionals can easily deploy lithium-ion UPSs without the maintenance and refresh challenges of those utilizing lead acid. The extended battery life provided by lithium-ion enables users to align their UPS refresh cycles with the rest of IT stack, saving time and money spent on labor and replacement batteries. Furthermore, lithium-ion UPSs boast a “set it and forget it” value proposition, which is especially conducive at sites where UPSs protect critical network operations yet IT resources are not extensive.

Are there small office/rackmount lithium UPS solutions available now on the market?

Yes, office-sized UPSs with lithium batteries are now available. Although more expensive than VRLA-powered UPSs, they are dramatically lighter and the battery will typically last the entire life of the UPS. Eaton offers two models of the 5P UPS with lithium-ion batteries: the 5P1500R-L, which is a 120V 1440 VA unit, and the 5P1550GR-L, which is a 208V 1550 VA unit. 

What are some of the downsides of lithium batteries compared to VRLA?

The primary downside is that because the technology is so new, many manufacturers have limited experience in UPS applications. However, this is changing rapidly, with successful deployments now exceeding three years. 

Do lithium batteries pose a higher fire risk than VRLA batteries?

While any battery has the potential to catch fire if abused, lithium has a reputation for more dramatic ‘thermal events.’ However, in UPS applications, the presence of a Battery Management System (BMS) — which controls charge rate, voltage and temperature — makes lithium batteries less likely to enter thermal runaway than traditional UPS batteries. Additionally, the manufacturing of lithium-ion UPS batteries is not as restrictive on packing size as other applications such as cell phone or laptop battery modules, which have appreciably constricted space. UPS manufacturers can utilize the extra space to ensure that the plates inside the battery will not short out, even in extreme conditions. As long as the battery and its packaging are designed to dissipate more heat than can be created on overcharge, the battery cannot go into thermal runaway.  All UPS vendors and battery vendors are ensuring that this is the case for lithium products.

Have Eaton lithium-ion UPSs experienced any battery failures or fires?

At this time, no UPS manufacturer has suffered a thermal event with its lithium batteries. The presence of a BMS has been instrumental in the detection and mitigation of any anomalies. While we have seen individual batteries fail to retain a charge, these rare instances were not thermal-related and occurred only after we abused the batteries in our lab with stress testing.  When the individual cells were replaced, the system operated correctly.  

Are lithium-ion batteries more expensive?

In general, they vary from slightly more expensive than good-quality VRLA, to two to three times more expensive, especially when shipping costs and commissioning services are considered. Lithium batteries can be sensitive to high temperatures during transit, requiring manufacturers to ship loose batteries in refrigerated trucks at a 30 percent state of charge (SOC). In addition, Eaton requires a customer service engineer to be on site for large battery cabinet startup service, which isn’t needed for VRLA batteries. 

It is important to note that in the near future, when vendors start shipping battery cabinets pre-loaded with batteries, we expect the shipping costs for lithium batteries will actually be slightly less than that of VRLA batteries. 

Are there different recharge rates between lithium-ion and VRLA batteries?

Lithium batteries can be recharged significantly faster than traditional UPS batteries; however, keep in mind that the manufacturers limit the amount of battery charge current that the UPS can supply.  During recharge, the BMS monitors not only voltage levels, but also the internal temperature of each individual lithium cell. In this manner, the system will automatically limit the charge if a cell gets too warm, which can potentially lengthen the recharge time. In general, the VRLA rule-of-thumb of “10x the discharge time to 90 percent capacity” will not apply to lithium.

What is the shelf life of lithium-ion batteries before they need to be checked or charged?

If the battery modules are connected together, i.e. installed in a cabinet, the storage times are six months at 25 degrees C. This is due to parasitic losses from the BMS.

If the battery modules are NOT connected together (either power or communication connections), then the storage times are one year at 25 degrees C. 

Note: Samsung requires a "voltage check" of the batteries every 180 days during storage.

Do lithium batteries work with Eaton ABM?

ABM is not needed with lithium batteries. The purpose of ABM is to extend the service life of VRLA batteries, and since lithium already has an excellent service life characteristic, there are no immediate plans to use it. 

Can lithium be mixed with other types of batteries (for example, VRLA)?

No, lithium cannot be put in series or parallel with other types of batteries.

Is there any difference between sizing a lithium-ion battery compared to VRLA or NiCd technology?

Yes, the sizing is slightly different and in the case of lithium, we limit the backup time based not only on low cell voltage limits, but also the cell temperature during discharge.  This means the cutoff time for a lithium battery might be dictated by high temperature, as opposed to only low voltage. Eaton’s published battery time tables for our UPS products take this into account, and our application engineers are trained on proper sizing of these batteries. As always, feel free to contact Eaton for sizing guidance.

What are the recommended testing protocols to include in 3rd party commissioning of a lithium-ion UPS battery system?

With the absence of a standardized commissioning test for lithium batteries, we expect that commissioning would be somewhat similar to that of VRLA, and should include the following:

  1. Verification of correct and safe installation per the vendor’s manuals, including torqueing of terminals and set up of the Battery Management System by a trained service engineer. Configuration files should be saved for future reference.
  2. Refresh charge to ensure all batteries in each string are properly voltage-balanced and within limits (this may require 48 to 72 hours of charging). Note that batteries may have been reduced to 30 percent SOC during shipment.
  3. Test discharge for time, at one or preferably two different UPS load levels, followed by a review of the BMS data, looking for temperature or voltage anomalies during the discharge.
  4. Take time to recharge data and record after a full discharge test.  Verify UPS charge limits are programmed correctly.
  5. Verify communication of status, and automatic disconnect device (breaker or contactor) in each cabinet to ensure it is functioning correctly.

Do lithium-ion batteries have recycling and/or disposal issues?

Lithium-ion batteries are disposable and, while currently not readily recyclable, new options are expected in the future. 

To read more about recycling lithium-ion batteries, visit Eaton's battery recycling page. 

What else can a UPS system do with the addition of lithium-ion batteries?

With lithium-ion, UPS operators can play a role in helping energy providers balance power generation and consumption with the EnergyAware solution. EnergyAware enables facilities to support sustainable energy solutions, optimize the cost of powering their buildings and create additional revenue streams from their power protection assets. Learn more at Eaton.com/EnergyAware. 

Can the UPS batteries be charged by the PV system, assuming the current is suitable? If not, what other back-up method would you suggest?

We recommend that the PV system (and its inverter) be fed to the UPS input so the UPS directly controls the battery recharging.  In the future this may not be necessary, but in these early applications it is important to have control over the rate of charge for the UPS batteries.