One of the most important features of a battery is how long it lasts. After all, there is a reason that Energizer has been advertising that their batteries “keep going, and going, and going” for the better part of 25 years…

But when it comes to investing in home battery storage, the stakes are much higher than picking a Triple-A battery to power your TV remote.

With tens of thousands of dollars on the line and dozens of solar battery brands to choose from, it’s worth taking a minute to consider which solar battery lasts the longest. In this article, we’ll explore which battery type lasts the longest and the best solar batteries to buy if longevity is your primary concern.

Design a custom solar & battery system from the comfort of your home.

What is the longest-lasting solar battery type?

The lithium-ion batteries that dominate today’s residential energy storage market have a usable life (70% capacity or more) of 10-15 years, which is roughly double the lifespan of the lead-acid batteries used in the past. However, the lifespan of a lithium-ion battery also depends on its chemistry and how you use it.

There are two lithium-ion battery chemistries that are especially widespread in today’s market:

• Lithium iron phosphate (LFP) is used in Franklin Homepower, sonnenCore+, Panasonic EverVolt, Enphase IQ, and SunPower SunVault batteries
• Lithium nickel manganese cobalt oxide (NMC) is used in LG ESS Home8, LG RESU Prime, Generac PWRcell, and Tesla Powerwall 2 batteries

In general, LFP batteries tend to last longer than NMC because they are more resistant to high temperatures that degrade battery life. However, the lifespan of a battery also depends on how you use it.

According to a 2020 study by the National Renewable Energy Laboratory (NREL):

• LFP batteries last longer in self-consumption mode, where the battery is charged with solar energy during the day and discharged to power household systems at night to avoid interaction with the grid
• NMC batteries last longer in backup mode, in which the battery maintains a high state of charge and is only discharged during grid outages

So, if you plan on charging and discharging your battery every day, an LFP will likely last longer. If you only plan on using your battery for backup power during grid outages, an NMC battery will likely last longer.

Next, we’ll look at some of the longest-lasting battery models for each chemistry type.

Longest-lasting solar battery models of 2023

Alright, so we’ve narrowed the longest-lasting solar batteries into two lithium-ion chemistries: LFP and NMC. Now let’s take a step further and look at some of the longest-lasting battery models for each chemistry based on the warranty terms offered by each manufacturer.

Battery warranties guarantee that a certain level of usable storage capacity will remain after a set number of years or usage, whichever comes first. Usage is measured in two ways:

• Cycles: The number of times a battery charges and discharges
• Energy throughput: The total amount of energy the battery charges and discharges

In 2023, a “standard” solar battery warranty is for 70% of nameplate capacity after 10 years and 3,000 to 4,000 cycles. The batteries on the lists below carry warranties that go above and beyond this standard in some way.

Longest-lasting LFP battery warranties

Lithium iron phosphate (LFP) has emerged as the longest-lasting battery type on the market, as indicated by 12 and even 15-year warranties (as opposed to the standard 10 years).

Some of the longest-lasting LFP batteries are listed in the table below.

*Unlimited cycle warranty may not be valid for “homeowners who charge over 5MWh from sources other than PV”

A few LFP battery warranties that stand out:

• Enphase is among the first manufacturers to offer a 15-year warranty
• SunPower is among the first manufacturers to offer an “unlimited cycle” warranty, but there is a clause that limits charging from the grid

Now, let’s see how the top LFP battery warranties compare to the top NMC battery warranties.

Longest-lasting NMC battery warranties

In general, the warranties for NMC batteries are shorter and cover less usage than the warranties for LFP batteries. The table below shows the warranty terms for the best NMC batteries on the market in 2023.

*Unlimited cycles warranty may not apply if the battery is charged using grid electricity.

A few things that stand out:

• We were not able to find an NMC battery warranty length beyond 10 years
• Tesla offers an “unlimited cycle” warranty on the Powerwall 2, however, it only applies to charging the battery with solar energy

Choosing the right solar battery

To recap, based on the manufacturer’s warranties (which tend to be conservative) you can count on today’s lithium-ion solar batteries to last at least 10 years – and perhaps up to 15.

However, your battery life is influenced by:

• Its chemistry (LFP vs NMC)
• How you use it (self-consumption vs backup)
• Its storage conditions (hot batteries = shorter lifespan)

Connect with an Energy Advisor to compare living pricing on the long-lasting batteries mentioned in this article.

As grid electricity gets more expensive and unreliable, homeowners are using solar and battery systems to reduce their energy costs and keep the lights on when the grid goes down.

But while sizing a solar system is pretty straightforward, choosing a battery size takes a bit of nuance and largely depends on how you plan on using it. In this article, we’ll explore the nuances of sizing a solar battery and lay out a process for determining the ideal battery size for your needs.

Team up with an Energy Advisor to design a custom solar and battery system for your home.

How to size a home battery

Home batteries are sized based on how many kilowatt-hours (kWh) of electricity they can store. There are two measurements to be aware of:

• Nameplate capacity is the maximum amount of electricity a battery can hold
• Usable capacity refers to the maximum amount of electricity the battery can discharge at once without exceeding the manufacturer’s recommendations for depth of discharge

For example, the SunPower SunVault 13 has a nameplate capacity of 13 kWh, but a usable capacity of 12 kWh after factoring in that only 92% of its full capacity can be discharged without affecting its lifespan. So, when choosing a battery size, make sure to focus on the usable capacity.

Next, follow three steps to figure out how many kilowatt-hours of electricity you want your solar battery to hold.

Step 1: Establish your energy goals

The first step to sizing your solar battery is determining which function(s) you would like it to perform. There are three basic roles battery storage can play:

• Critical loads backup: Powering a select number of essential electrical systems during grid outages
• Whole-home backup: Powering the entirety of your home electrical systems during grid outages
• Self-consumption: Storing excess solar power produced during the day to avoid buying expensive electricity from the grid at night

Historically, home battery systems are most associated with critical loads backup. However, with time-of-use rates becoming more common and net metering policies eroding across the US, using battery storage for solar self-consumption is gaining popularity as a cost-saving strategy.

There may be cases in which you can use a single battery system for two purposes. For example, if you have a 10 kWh backup battery you may also be able to use it for solar self-consumption (with the understanding that you won’t get much or any backup power if the grid goes down shortly after your battery has been discharged).

So, let’s say your primary goal is to power critical systems during grid outages. What’s the next step to determining the right battery size?

Step 2: Determine the size of the load

The next step to sizing your solar battery is determining the maximum load you want it to power. In other words, figure out:

• Which systems you want to back up
• How much electricity they consume
• How long you want to be able to power them

For example, if your goal is to power critical systems during grid outages, then the first step is to identify those systems. These systems typically include:

• Refrigeration
• Medical devices
• Lights
• Fans
• TV, Wi-Fi, and device charging
• Kitchen appliances
• Water heating

Air conditioning and electric heat consume a ton of electricity and therefore typically aren’t included in essential battery backup systems. But smaller systems, like the ones listed above, are routinely backed up by home solar and battery.

Next, you’ll make a “loads list” that adds up how much electricity each system uses. This will start to give you an idea of how much capacity you’ll need to power these systems on battery power alone.

Pro tip: Google “(refrigerator model) wattage” or check the labels on your appliances to determine the power needs of your critical backup loads.

Example critical loads list for battery backup

*The figures above are averages and are meant for example use only. Check the power rating for your specific devices when creating a loads list.

In this scenario, the battery is responsible for around 10 kWh of critical backup loads over a 24-hour period.

Step 3: Choose how long you want to power your loads

The final step is to determine how long you want to be able to power these systems with battery storage alone – known as “days of autonomy.” Ideally, your solar panels will charge your battery during the day, but it may be worth planning for scenarios in which snow, cloudy weather, and short winter days limit your solar production.

For what it’s worth, the average utility customer in 2021 experienced 1.42 power outage events per year that lasted more than 7 hours on average (up from 3.5 hours per outage in 2013), according to data from the EIA. But there have been 28 outages that lasted 10 hours or more in the first 9 months of 2023 alone.

The size of your battery is essentially a product of your critical backup needs and your desired days of autonomy, as shown in the chart below.

It’s worth noting that a Lawrence Berkeley National Laboratory study found that 10 kWh of battery storage paired with a small solar system can meet critical backup needs for three days in most climate zones and times of year in the US.

What size solar battery do I need?

Choosing a battery size is more of an art than a science because it requires a balancing act between your goals, critical electricity needs, and budget. As a rule of thumb, 10 kWh of battery storage paired with a solar system sized to 100% of the home’s annual electricity consumption can power essential electricity systems for three days.

You can get a sense of how much battery capacity you need by establishing goals, calculating your load size, and multiplying it by your desired days of autonomy.

Or, connect with an expert Energy Advisor to design a custom system for your energy needs.