When selecting the correct battery for your needs, you may need to meet specific criteria, such as the required voltage, capacity, and whether the application is cycling or standby. Once these details have been determined, you may wonder, “Should I choose a Cohen lithium battery or a traditional sealed lead acid (SLA) battery?” More importantly, “What is the difference between lithium and sealed lead acid batteries?” There are many factors to consider, as both battery types have advantages and disadvantages.
For this article, “lithium” refers to lithium iron phosphate (LiFePO4) batteries, while “SLA” refers to lead acid/sealed lead acid batteries. Below, we will discuss the performance differences between these two types of batteries.
One of the significant differences between LiFePO4 and lead-acid batteries is that the capacity of LiPo batteries remains constant regardless of the discharge rate. The graph below shows the relationship between actual capacity as a percentage of rated capacity and discharge rate (C rate). At high discharge rates, such as 0.8C, lead-acid batteries maintain only 60% of their rated capacity. In cycling applications where discharge rates typically exceed 0.1C, lithium batteries with lower rated capacities outperform comparable lead-acid batteries. While the initial cost of lithium batteries is higher, the same applications require less battery capacity and are more economical. Considering cycle life, lithium batteries are more cost-effective than lead-acid batteries.
Another key difference is cycle performance. In most cases, Li-ion batteries have ten times the cycle life of SLA batteries, which reduces the cost per cycle and frequency of battery replacement in cycling applications.
Constant Power Output: Lithium Batteries vs Lead Acid Batteries
Unlike Li-ion batteries (such as those manufactured by Cogent), which can deliver constant power throughout a discharge cycle, SLA batteries start with plenty of power and then taper off. The graph below shows the relationship between voltage and state of charge, highlighting the constant power advantage of lithium batteries. Lithium batteries maintain a stable voltage throughout discharge, ensuring continuous power output. Specifically, this means that a flashlight powered by Li-ion batteries stays bright from start to finish, while a flashlight powered by SLA batteries dims as the batteries run out.
Charging Time: Li-Ion vs SLA Batteries
SLA batteries are known to charge very slowly. In cycling applications, a backup battery is often required to keep things running while charging. In standby applications, SLA batteries require constant float charging. Kaihen lithium batteries charge four times faster than SLA batteries, minimizing downtime and reducing the required batteries. Their ability to recover quickly after an event makes them more efficient and reliable in various applications.
Lithium Battery Performance in Backup and Standby Applications
Lithium batteries offer significant advantages in backup or standby applications. One of the key advantages is that there is no need to float charge the lithium battery during storage. For a detailed description of lithium battery charging, please refer to our Lithium Battery Charging Guide.
High-Temperature Battery Performance
Li-ion batteries excel in high-temperature environments, far outperforming SLA batteries. For example, at 55°C, lithium batteries have twice the cycle life of SLA batteries at room temperature. In most cases, Li-ion battery performance is excellent.
Lithium Iron Phosphate Battery Cycle Life vs. Temperature
Low-Temperature Battery Performance
Cold temperatures cause a significant reduction in capacity for all battery types. Two key factors must be considered when evaluating a battery’s suitability for cold weather use: charging and discharging capabilities. Lithium batteries cannot be charged below 32°F, while SLA batteries can handle low current charging even in freezing conditions.
On the other hand, Li-Ion batteries have a higher discharge capacity at low temperatures than SLA batteries. This means that while charging can be challenging, Li-ion batteries do not need to be over-engineered for cold environments. At 0°F, Li-ion batteries can discharge up to 70% of their rated capacity, while SLA batteries can only reach 45%.
It is essential to consider the condition of the Li-ion battery before charging it in cold temperatures. If the battery has just completed a discharge cycle, it will generate enough heat to receive a charge. However, if the battery has cooled and is below 32°F, it may not be able to accept a charge.
Battery Installation
Lead-acid batteries can be tricky since they cannot be installed upside down to avoid venting problems. While SLA batteries are designed to minimize leakage, they still have venting holes that release some gas. In contrast, lithium batteries have individually sealed cells that prevent leakage and allow unrestricted mounting orientations. Lithium batteries can be mounted sideways, upside down, or upright without concern.
Battery Weight Comparison
Lithium batteries are, on average, 55% lighter than SLA batteries. The weight advantage is significant in bicycle applications, such as motorcycles, scooters, or electric vehicles, where weight can significantly impact performance. In standby applications, the weight factor is critical for remote installations, such as solar fields, or hard-to-reach areas, such as emergency lighting systems.
SLA and lithium battery storage
Regarding storage, Li-Ion batteries should not be kept at 100% state of charge (SOC), whereas SLA batteries must be kept fully charged. This is because SLA batteries self-discharge at five times the rate of lithium batteries. Many users keep SLA batteries at 100% via a trickle charger to prevent reduced battery life.
Series and Parallel Battery Installation
When installing batteries in series or parallel, remember that all batteries must match various factors, including capacity, voltage, resistance, state of charge, and chemistry. It is important to note that SLA and lithium batteries cannot be mixed in the exact string.
SLA batteries are often considered “dumb” batteries compared to Li-Ion batteries because Li-Ion batteries have a built-in circuit board for monitoring and protecting the circuit board. This allows SLA batteries to handle more cells in series than lithium batteries. The length of a LiPo battery in series is limited by the circuit board components, which have specific current and voltage limits that may be exceeded if the series is longer. For example, a series battery pack of four lithium cells has a maximum voltage of 51.2 volts. In addition, battery protection is a key consideration.
Exceeding the specified protection limits for a single cell may disrupt the charging and discharging process for the entire battery pack. Most lithium battery packs contain a maximum of six or fewer cells (depending on the model), but more extended configurations are possible with additional engineering.
Significant differences exist between the performance of SLA and LiPo batteries. In general, lithium batteries outperform SLA batteries. However, SLA batteries should not be overlooked. They still have an advantage in some cases, such as longer strings, extremely high discharge rates, and low-temperature charging. Please get in touch with us if you have a specific application not covered here or have additional questions.