Lithium Batteries vs Lead Acid Sealed or Flooded.

Over recent years, lithium-ion batteries have surged in popularity and overtaken lead-acid batteries as the preferred option for storing you energy. But this does not mean the lead-acid battery is dead. Lead-acid battery technology is still advancing, with the release of high performance sealed tubular Gel batteries.

In this review, we compare two popular lithium-ion (LFP) batteries with a general idea of how they operate.  A direct comparison is not easy as each battery type behaves differently depending on the rate of discharge, depth of discharge, and cycle life required. .

Note, This review does not include unsealed or flooded Lead Acid Batteries as they require high levels of maintenance, specially ventilated area’s, and any cost savings can be outweighed by regular maintenance work required throughout the life of the battery.

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Lithium-ion batteries are now widely regarded as the best battery type for general energy storage applications due to their high energy density and very high efficiency. However, there is more than one type of lithium battery available. Most lithium batteries used for home energy storage generally use lithium iron phosphate (LiFePO4 or LFP) cells due to the lower cost and long cycle life. However, several well-known manufacturer’s such as Tesla and LG use Lithium NMC cells  For this review, we focus on Lithium LFP batteries since Flooded is another whole different specs and with needed venting this to us is no longer an Option on a Boat and RV

Battery Efficiency

Battery efficiency, also known as round trip efficiency, is the charging and discharging efficiency or loss during use. Due to the laws of physics, the transfer of energy from one form to another results in energy loss. In this case, the transfer is from electrical to chemical energy during battery charging and chemical back to electrical during discharge. Generally, losses from lead-acid batteries are much higher at 15-20% while most lithium-ion batteries are significantly lower at 2-8%.

• Deep-cycle lead-acid efficiency = 76% - 85%

• Lithium LFP battery efficiency = 92% - 98%

Another problem with lead-acid or lead-carbon battery systems is the longer charge time compared to lithium systems. A lead-acid charge cycle (bulk-absorption stages) can take 2 to 4 hours, depending on the depth of discharge. This means during bad or intermittent weather the charge efficiency can be very low and a full charge may not be achieved which can reduce battery life. In contrast, lithium batteries can charge very quickly, in 1 to 2 hours, and can efficiently absorb energy at much higher rates. Also unlike lead-acid batteries, lithium-ion batteries can tolerate partial state of charge (POS) for long periods of time without degradation or sulfation issues. Incomplete charging of lead-acid batteries on a regular basis (which can occur over winter) can significantly reduce the life of most lead-acid (AGM or Gel) batteries.

Battery Capacity - Depth Of Discharge

Battery capacity is measured in either Amp Hours (Ah) or kilowatt-hours (kWh). The amount of energy used, known as the depth-of-discharge or DOD is taken as a percentage % of total battery capacity, refer to the diagram below.

To convert Ah to kWh simply multiply the battery Ah rating by the total battery bank voltage. For example a 24V lead-acid battery bank made up with 12 x single cell (2v) 600Ah batteries: 12 x 2V x 600Ah = 14,400Wh. This can then be divided by 1000 to convert to kilowatt hours - 14.4kWh total capacity.

As a general guide, lithium (LFP) batteries are designed to be discharged up to 90% total capacity (10% SOC) while the traditional Lead (Gel and AGM) are generally not discharged more than 30-40% on a daily basis, unless in emergency backup situations.

Usable battery capacity comparison

Maximum daily depth of discharge (DoD) allowed **

• Lithium-ion = 80 to 90%

• Lead-acid AGM = 20 to 30%

• Lead-acid Gel = 20 to 40%

• Lead-Carbon = 20 to 50%

** Always refer to manufacturers specifications. Warranty may be void if deep discharge occurs below what is specified by the manufacturer’s warranty conditions.

Lead-acid battery capacity

Advanced tubular gel and lead-carbon batteries are more durable than traditional gel and AGM batteries and can sustain greater depth-of-discharge, with up to 70% available (in backup situations). However, battery cycle life will be severely reduced if deep discharges occur on a daily basis. It is recommended to set a maximum depth of discharge to no more than 40% for lead-acid and lead-carbon batteries, and a maximum of 70% in backup situations. Lithium-ion batteries on the other hand can generally be discharged from 70-90% on a daily basis, and 95 to 100% in backup situations*

* Always refer to battery manufacturers specifications.

We would like to hear from you with success stories or may some insight on both styles of Batteries.