The usable capacity of a battery refers to the amount of stored energy that can be safely discharged without causing significant degradation or damage to the battery. It is usually expressed in terms of the battery’s state of charge (SOC), ranging from 0% (empty) to 100% (Full).

What to consider when replacing Lead Acid batteries with Lithium Iron Phosphate (LiFePO4) Batteries: 

Lithium Iron Phosphate batteries offer numerous benefits over Lead Acid Batteries including a longer lifespan, higher energy density, higher efficiency, faster charging, and low maintenance. <see this blog post here for more details and a comparison between Lithium Iron Phosphate >.

When replacing a Lead Acid battery with a Lithium Battery, it is important to choose the correct capacity battery for your application. The usable capacity of each type of battery plays a big role in this decision.

LiFePO4 batteries have a high usable capacity, typically they can safely discharge up to 100% of the stored energy without compromising the battery’s health and will still deliver the expected or warranted lifespan.

Lead Acid batteries have a low usable capacity, typically 50% of their total capacity. This means that they can safely discharge only half of the stored energy without compromising the battery’s health or longevity.

This means that a 12v100Ah deep cycle lead acid battery can be replaced with a 12v50Ah lithium battery and still have the same usable capacity. You could get more energy from a 12v100Ah lead acid battery than a 12v50Ah Lithium battery, but then you are damaging the battery and it will shorten its already short lifespan further. Also, if a Lead Acid battery is ever drained very low, it will be damaged internally and have a lowered ability to store energy.

<see our blog about DOD, you can extend the life of a lithium battery by 2.5 times if you only do 50% DOD  >

The usable capacity of LiFePO4 batteries is influenced by various factors, including the battery’s design, discharge current, and temperature. Higher discharge currents may slightly reduce the usable capacity due to increased internal resistance and voltage drop. Similarly, extremely low or high temperatures can affect the battery’s performance and usable capacity.

While they may have a higher upfront cost, their superior performance and longer lifespan make them a more cost-effective option in the long run. If you’re considering a new battery for your application, you should consider Lithium Iron Phosphate as an alternative to Lead Acid batteries.