Solar lithium batteries are broadly classified into two categories: lithium-ion and lithium polymer. Lithium-ion solar batteries have distinct chemistries: lithium iron phosphate (LFP or LiFePO4), lithium nickel manganese cobalt oxide (NMC), lithium manganese oxide (LMO), etc.
How long solar lithium batteries last depends on the chemistry, cycle life, and usage. A LiFePO4 solar lithium battery can last ~10 years, whereas a lithium polymer (Li-Po) power bank may work only half that long. Some LiFePO4 solar batteries may last up to 15 years.
Plenty of factors determine how long your solar lithium batteries are likely to last, including how you recharge and discharge them. Plus, not all brands make high-quality or long-lasting solar lithium batteries. Read on to know more about the longevity of solar lithium batteries.
How Long Solar Lithium Batteries Last Depends on the Cycle Life
The following solar lithium batteries are relatively new and rare in residential solar systems:
- Lithium manganese oxide (LMO)
- Lithium nickel cobalt aluminum oxide (NCA)
- Lithium nickel manganese cobalt oxide (NMC)
You are likely to use a solar battery with lithium iron phosphate chemistry (LFP or LiFePO4) or a power bank using lithium polymer (Li-Po). So I will confine the scope of this post to these two types of solar lithium batteries.
The primary factor determining the longevity of a solar lithium battery is its cycle life.
All solar lithium batteries have a cycle life, which is clearly stated by the manufacturers. This attribute is a dynamic factor, not a constant in all circumstances. However, solar lithium batteries won’t function optimally beyond the cycle life.
Consider the bestselling Ampere Time LiFePO4 Deep Cycle Battery (available on Amazon.com). This solar lithium battery has variants rated for different amps per hour and volts, including the following:
- 12V 100 Ah
- 12V 200 Ah
- 12V 300Ah
- 12.8V 6 Ah
- 48V 100 Ah
These Ampere Time solar lithium batteries are rated for 4,000+ cycles. Thus, if you charge one of these once every day, you are looking at more than 10 years of service life.
Ampere Time’s solar lithium batteries have 100% depth of discharge (DOD) and 100% state of charge (SOC). Hence, you don’t have to worry about these lithium-ion batteries not discharging at a low charge or the LiFePO4 chemistry impairing the recharging to a level short of 100%.
LiFePO4 Solar Lithium Batteries Will Outlast Li-Po Power Banks
Compare the ~10 years cycle life of LiFePO4 with solar lithium polymer batteries or Li-Po power banks. Let me use the example of the bestselling MREGB Solar Power Bank (available on Amazon.com). The 42.8 Ah solar charger and power bank’s Li-Po battery is rated for 1,600+ cycles.
Hence, solar lithium polymer batteries last half as long or shorter than lithium-ion variants, such as LiFePO4. This shorter cycle life doesn’t mean the MREGB solar power bank is completely inferior to the Ampere Time battery. Both are durable and reliable with several great features:
- Protections: overcharge, short circuit, temperature, etc.
- Shock-proof or vibration-resistance design
- Waterproof construction (rated for IP65 or IP67)
Having said that, LiFePO4 batteries are superior in many ways. LiFePO4 can store a lot more charge and power many devices simultaneously. LiFePO4 doesn’t suffer from memory effects that are common for Li-Po batteries. And, of course, LiFePO4 lasts twice as long or longer.
Solar Lithium Batteries Continue To Function After the Cycle Life
Ampere Time’s LiFePO4 deep cycle battery is rated for up to 8,000 cycles. 4,000 cycles are the minimum you can expect for the battery to operate flawlessly, which means at optimum capacity. Subsequently, solar lithium batteries continue to function but at suboptimal capacity.
In other words, Ampere Time solar lithium batteries may not operate at 100% state of charge or depth of discharge after 4,000 cycles up to 8,000 cycles. But the batteries will function. So such batteries can last longer than 10 years, sometimes up to 15 years at suboptimal capacity.
Consider the example of the Weize LiFePO4 Lithium Battery (available on Amazon.com). The Weize solar lithium batteries have different amp-hour capacities and are rated for up to 8,000 cycles. But that doesn’t mean such a battery will last 20 years or longer.
The Weize solar lithium batteries are rated for 2,000+ cycles if you discharge them completely. The maximum potential of 8,000 cycles is applicable only if the depth of discharge is 50% on average when you recharge the battery.
Otherwise, these Weize batteries won’t perform at optimum capacity after 2,000 cycles. So, the batteries will have a shorter life than Ampere Time’s variants with 4,000 to 8,000 cycles, which isn’t surprising given the latter cost almost twice as much as Weize.
In the context of similarities, both Ampere Time and Weize offer a 5-year warranty covering any battery defects due to manufacturing or quality issues. Compared to these two brands, CHINS offers a much more comprehensive warranty and coverage.
The CHINS 24V 200Ah Lithium Battery (available on Amazon.com) offers the following assurances:
- Money back guarantee or refund within 90 days
- Free replacement within 3 years from the shipping date
- Free maintenance and support for the first 120 months
This CHINS LiFePO4 solar lithium battery is rated for 2,000+ cycles. It can last up to a decade, depending on your frequency of use, once it is beyond the rated cycle life. These types of solar lithium batteries tend to have a low self-discharge rate of ~2% per month.
Factors That Reduce the Life of a Solar Lithium Battery
The chemistry of LiFePO4 cells is vulnerable to thermal runaway. However, modern solar lithium batteries using LiFePO4 cells have many protective features, such as against:
- Extreme temperature
Still, most solar lithium batteries will not last long in either freezing or scorching conditions. Most manufacturers have an operating temperature range for both charging and discharging.
Ampere Time’s operating temperature range for charging is 32 to 122 °F (0 to 50 °C). The range for optimum discharging is -4 to 140 °F (-20 to 60 °C). Weize has a similar range, but the upper limit for its charging is 113 °F (45 °C).
Likewise, most manufacturers recommend a few best practices, including but not limited to the following:
- Charging or recharging only after discharging up to a certain level, such as 20%.
- Storing a solar lithium battery at more than 50% charge when it is not in use.
- Fully recharging once in 90 to 180 days when the battery is not in use or stored.
If you don’t follow the best practices and manufacturer’s recommendations, your solar lithium batteries are unlikely to last 10 years or anywhere close; leave aside extending its life. These batteries can suffer permanent damage if you keep or store them in a fully discharged state.
Solar lithium batteries of reasonably good quality should last 10 years at optimum capacity and longer with some performance issues, such as reducing the state of charge, low discharge, etc. But expect this longevity only if you follow the best practices and manufacturer’s instructions.
- Elum Energy: Solar + Storage – Battery Types for Solar Systems
- RAVPower: Lithium Ion vs. Lithium Polymer Batteries – Which Is Better?
- LithiumHub: What Are LiFePO4 Batteries?
- Canbat Technologies Inc: How To Store LiFePO4 Batteries
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