What are the main benefits of switching to lithium UPS batteries?
The most common reason is a significant increase in service life. Lithium also offers longer cycle life (charge/discharge cycles range from thousands to thousands, compared to about 500-600 charge/discharge cycles for VRLA batteries), as well as a longer warranty. Additionally, lighter weight and a smaller footprint are added benefits.
Additionally, IT professionals can easily deploy lithium batteries in UPS without the maintenance and refresh challenges associated with lead-acid batteries. Lithium batteries last longer, allowing users to align UPS refresh cycles with the rest of the IT stack, saving time and money spent on labor and battery replacement. Additionally, lithium batteries in UPS have a “set it and forget it” value proposition, which is especially beneficial for sites where the UPS protects critical network operations but where IT resources are not abundant.
What are the disadvantages of lithium batteries compared to VRLA?
The main disadvantage is that many manufacturers have limited experience with UPS applications because the technology is so new. However, this is changing rapidly, and large battery brands like EverExceed are now stepping up to produce reliable lithium batteries.
Are lithium batteries a higher fire risk than VRLA batteries?
While any battery has the potential to catch fire if abused, lithium batteries are known for more severe "thermal events." However, in UPS applications, the presence of a battery management system (BMS) that controls charge rate, voltage, and temperature makes lithium batteries less susceptible to thermal runaway than traditional UPS batteries. Additionally, the manufacturing of lithium-based UPS batteries does not impose packaging space constraints like other applications such as cell phone or laptop battery modules where space is obviously constrained. UPS manufacturers can use the extra space to ensure that the plates inside the battery do not short out even under extreme conditions. As long as the battery and its packaging are designed to dissipate more heat than is produced when overcharged, the battery will not experience thermal runaway. All UPS vendors and battery suppliers ensure that the same is true for lithium products.
In addition, EverExceed recommends that customers use LFP batteries instead of NCM batteries in UPS applications because LFP is much safer than NCM based on the chemical reaction. Lithium iron phosphate batteries can guarantee that you will not catch fire or explode.
Are lithium batteries more expensive?
Generally speaking, their prices range from slightly more expensive to twice as expensive as high-quality VRLA, especially when shipping costs and commissioning services are taken into account. It’s worth noting that in the near future, when suppliers start shipping battery cabinets with pre-installed cells, we expect that shipping costs for lithium batteries will actually be slightly lower than VRLA batteries. You also need to note that lithium batteries have a much lower TCO than VRLA batteries, and within a few years you will get much more from your lithium battery investment than VRLA.
Do Lithium and VRLA batteries charge at different rates?
Lithium batteries charge significantly faster than traditional VRLA UPS batteries; however, keep in mind that manufacturers limit the amount of battery charging current a UPS can provide. During charging, the BMS not only monitors voltage levels but also the internal temperature of each lithium battery. This way, if the battery overheats, the system will automatically limit charging, which may extend charging time. In general, the VRLA rule of thumb "10x discharge time to 90% capacity" may not apply to lithium.
What is the shelf life of lithium batteries before they need to be inspected or recharged?
If the battery modules are connected together, i.e. installed in a cabinet, the storage time at 25°C is six months. This is due to parasitic losses in the BMS.
If the battery modules are not connected together (power or communication connection), the storage time at 25°C is one year.
NOTE: It is recommended that the battery be "voltage checked" every 180 days during storage.
Can lithium be mixed with other battery types (such as VRLA)?
No, lithium cannot be used in series or parallel with other battery types.
Is there any difference in the size of Li-ion batteries compared to VRLA or NiCd technology?
Yes, the dimensions are slightly different, and with lithium batteries we limit the backup time not only based on the low battery voltage limit, but also the battery temperature during discharge. This means that the cut-off time of a lithium battery may be determined by high temperature, rather than just low voltage. As always, please feel free to contact EverExceed for sizing guidance.
Are there recycling and/or disposal issues with lithium batteries?
Lithium batteries are disposable and although currently not easily recyclable, it is expected that there will be new options in the future.
Can UPS batteries be charged by a photovoltaic system if the current is appropriate? If not, what other backup methods do you recommend?
We recommend feeding the PV system (and its inverter) to the UPS input so that the UPS controls battery charging directly. This may not be necessary in the future, but in these early applications it is important to control the charging rate of the UPS batteries.
