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Sealed Lead Acid vs Lithium-Ion Batteries

Published by Lee Kelly on 03 February 2020

There are a few types of batteries that are used for UPS, renewables and demand response systems. The first and most prevalent type is sealed lead-acid (SLA/VRLA for short). The other type that is gaining traction very rapidly with a lot of help from Tesla is Lithium-Ion. Both batteries have positives and negatives within the space and I am here to compare them for you.

Seal Lead Acid Batteries

Sealed lead-acid batteries have been the norm in a lot of backup systems for years and are really effective with around 80-85% efficient when charging with the rest is not being stored and unable to be used. SLA/VRLA batteries being around for so long and the most popular choice, for the most part, means that the batteries are usually fairly cheap. Most SLA/VRLA batteries have a life span of 3-5 years and a limited number of cycles which varies by brand perhaps less than 300 but this can be up to 12+ depending on the manufacturing process. While effects of the environment, cycles and deep discharging all play an effect on the actual life span of an SLA/VRLA battery.

Critical Power Supplies - Sealed Lead Acid batteries

Lithium-Ion Batteries

Lithium-Ion batteries have been around for a while but they have only recently gained lots of traction with UPS and backup power systems. With only a few manufacturers creating a lithium-ion system (APC and Eaton are some of the manufacturers who have systems). The new technology that has been developed within lithium batteries means that you can put the batteries through deeper cycles. Lithium-Ion batteries also have a very high-density rate meaning you can get a longer charge out of a smaller battery. A typical lifespan of a Lithium-Ion UPS Solution can be 2-4 times that of a Standard VRLA battery making the higher initial upfront investment beneficial saving costs of VRLA replacement and potentially expensive downtime/engineering time.

Critical Power Supplies - Lithium-ion Cell

Comparison between SLA/VRLA and Lithium-Ion Chart

We have prepared this little table to show the comparisons between SLA/VRLA and Lithium-Ion Batteries. The details in this table are based on the norm and there may be a few outliers that don’t fall into these spaces.

Sealed Lead Acid Lithium-ion

Initial cost per capacity ($/kWh)



Number of cycles to 80% SOH

200 - 650

1000 - 4000

Typical state of charge window



Temperature Sensitivity

Degrades above 25 Degrees Celsius

Degrades above 45 Degrees Celsius

Batteries and which is better?

There are positives and negatives for both types of batteries but which battery that you choose will depend on what your uses case is. Lithium may work better for more consistent and higher battery usage while sealed lead acid may work better for short discharges and infrequent uses. It all depends on your application, lifespan + cost model budget and the TCO (Total cost of ownership) model you are looking to explore and work through.

Five things affect how a battery performs in the field.

  • For a VRLA how much lead is in the battery and its purity, not all batteries weigh the same.
  • Temperature they are used at.
  • Internal Resistance builds up.
  • Charge rate.
  • The number of cycles.

If you require more information then give our expert team a call on 0808 164 0608 or drop them an email here.