Battery warranties: What you need to know

Like your laptop or cell phone battery, solar batteries degrade over time: As you continue to use and charge your battery, it loses the ability to hold a charge. Fortunately, solar battery manufacturers provide warranties that guarantee the performance of a battery to a certain level. We'll dive into what matters in a solar battery warranty and how some top solar battery companies – Tesla Powerwall, LG Chem, and Sonnen – stack up.

Battery system warranties at a glance

Industry standard: You'll get at least ten years of coverage with most battery systems. However, your coverage may not last that long if you hit specific usage outputs first.

As you're comparing the warranty of one battery versus another, here are some of the most important factors to consider:

Warranty years

Nearly all battery manufacturers provide a warranty guaranteeing a battery's performance for a set amount of years. Across manufacturers, these warranty terms can vary, especially regarding batteries of different chemistries: Lead-acid batteries generally have a shorter lifespan than lithium-ion batteries and, therefore, shorter warranty periods. As you compare battery warranties, you'll find that many lead-acid products have warranties under five years, while most lithium-ion battery manufacturers offer warranties of ten years or more. Many battery warranties will also include a clause suggesting that the term could be shorter depending on your battery use – this is where cycles and throughput come into play.

Cycle life 

Most homeowners taking advantage of solar-plus-storage systems charge and drain their batteries daily – this is known as a "cycle." In addition to guaranteeing battery life for a set amount of years, some manufacturers also provide a warranty for guaranteed performance over a certain number of cycles. Similarly, the number of cycles your battery is warrantied for (if any) often depends on the battery's chemistry. Generally, lithium-ion batteries can withstand more cycles, so they should have a higher cycle count in their warranty agreements than lead-acid competitors. 

But read this line carefully: Manufacturers often guarantee a fixed product term OR a minimum number of cycles, whichever comes first. If you hit the warrantied number of cycles (e.g., 10,000 cycles) before your battery hits its 10th birthday, it could end your warranty term.

Evaluating battery warranties on more than just their cycle ratings is important. Solar batteries gradually lose their ability to hold a full charge as they age, which means a cycle toward the end of your battery's life will store and produce less energy than the output of a cycle immediately after installation. Additionally, the size of the battery is an important factor to compare along with cycles. A smaller battery that has a lifespan of 10,000 cycles may deliver less energy over its lifespan than a larger battery warrantied for only 7,000 cycles. That's why it's also important to consider a battery's throughput warranty.

Throughput

A throughput warranty is the total energy a manufacturer expects the battery to deliver throughout its lifetime. These warranties are typically stated in terms of megawatt-hours (MWh). Suppose a battery manufacturer provides a throughput warranty of 20 MWh. This means the warranty is valid until the battery stores and delivers 20 MWh–or 20,000 kilowatt-hours (kWh)–of energy. Like a cycle life warranty, throughput warranties typically only apply if your battery delivers a set amount of energy before its warranty period (i.e., ten years) is up. 

Because the output from cycling your battery will diminish as the years go on, it's difficult to estimate how much MWh of energy your warranty provides based on warrantied cycles alone. Throughput warranties are a more tangible metric, allowing you to assess the value of your battery over its lifespan more easily. It's hard to give you an exact number for what to expect for a throughput warranty because the numbers vary quite a bit depending on the overall storage capacity of your system. If your battery system contains several different battery cells–or modules–within it, your warranty may state a throughput by cell (which you can multiply by the number of cells to get the total throughput).

Industry standard: Many manufacturers will guarantee that your battery will still hold at least 60 percent of its original capacity by the end of your warranty term.

In addition to providing a warranty for a set number of years, cycles, or throughput, select manufacturers also offer an end-of-warranty capacity rating. This guarantees that your battery will hold a certain amount of capacity throughout the warranty. For example, LG Chem guarantees that by the end of 10 years or the warrantied throughput (whichever comes first), its battery will still hold 60 percent of its original capacity. Given the size of the LG Chem RESU 10H (9.3 kWh), this means roughly 5.6 kWh of capacity at the end of the warranty period. Higher percentages are better than lower percentage guarantees when comparing the end-of-warranty capacity ratings across various batteries.

Industry-standard: many manufacturers do not cover labor costs as a part of their warranty agreement.

As we mentioned above, battery companies should cover a replacement battery if you need it during their warrantied term. While the manufacturer may cover your replacement part, that doesn't necessarily mean they'll cover the labor costs to re-install that equipment. In fact, many manufacturers do not reimburse for labor associated with diagnostics, replacements, or repairs of their products.

Depending on the installer you move forward with, this addition–or omission–to a warranty could be moot: some local installation companies will cover maintenance and repair costs within their own workmanship warranty. Like equipment warranties, installer warranties vary from one company to the next and often only cover their own installation work – not maintenance costs for properly-installed equipment. 

When battery companies cover labor, they may only do so for a certain amount of time or a certain travel distance (e.g., three hours of driving). Those covering costs for replacements or repairs often require some form of sign-off from the manufacturer before proceeding with the fix.

Industry standard: Some companies cover shipping costs for replacement equipment, but not all of them.

Say your battery system breaks, and you can get a free replacement under your manufacturer's material warranty. Is the shipping included as well? 

This is an aspect of the maintenance process overlooked in some warranties. Many battery manufacturers will cover the material costs associated with the replacement part but not necessarily the fees to ship the equipment. Alternatively, they may be able to ship the product to a local or regional distributor but then require you or your installer to get that product to your home.

Industry standard: Most battery manufacturers leave workmanship warranties to the installer.

More often than not, installers are the sole party responsible for providing workmanship–or labor–warranties for your battery installation – they're performing the installation work, after all! However, it's becoming increasingly common for manufacturers to offer an extra safeguard by tacking on their own workmanship warranty coverage. When applicable, it's typically only an option if you work with specific installers in a manufacturer's certified network: they're putting their brand name and reputation behind their work and want to make sure they can stand by the installer performing the installation.

Industry standard: Every warranty–including battery warranties–has limitations and exceptions.

Battery warranties often come with a list of limitations and exceptions. These limitations aren't meant to make it difficult for you to take advantage of the offering; at the end of the day, companies need to protect themselves from unreasonable claims. 

Warranty limitations and void clauses vary from company to company, but here are a few to keep an eye out for:

• Transferability: If someone buys your home, will you be able to transfer the warranty over to them? Will you have to pay a fee to transfer the warranty?

• Installer endorsement: Do you need to work with a certified installer to take advantage of the warranty offering? If someone outside their network repairs your system, does that void your warranty claim? Is the warranty void if you perform a DIY installation?

• Outdoors vs. indoors installation: Do you want to install your battery indoors or outdoors? Not all battery systems allow for both, and installing it in a location not certified for use may void your warranty. You should also understand if you must keep your battery within certain temperature limits – outside or otherwise.

• Proximity to the ocean: Live on a beachfront property? (Lucky!) If so, make sure that this won't void your warranty. Saltwater can corrode casings around battery systems, so some manufacturers will void a warranty if their products are within a certain distance from saline bodies of water. 

• Acts of nature: This is a common one – most battery system manufacturers will not cover any damage caused by extreme weather events outside their control, such as hurricanes, floods, earthquakes, etc. Fortunately, the hardware is pretty durable and can withstand most storms without the added protection. Even better, many homeowner insurance policies cover damage to solar-plus-storage systems if damage occurs during a storm.

Industry standard: There isn't one! Reputation and warranty fulfillment standards and processes vary from company to company.

Let's say you need to submit a warranty claim – can you do that easily? And will the manufacturer stand by their warranty?

When you're comparing one battery warranty to another, also consider the following:

• How old is the company providing the warranty? Is it a bankable company, and do they have their own insurance policies or escrow that ensure their warranties will be upheld, even if they go out of business?

• Who's on the hook for actually fulfilling the warranty? Does the manufacturer have a parent company or subsidiary that backs the warranty? Do they process claims internally?

• How easy is it to make a warranty claim? Does the manufacturer allow you to submit the claim directly, or do you need to contact your installer? Does your installer need to come to your property and perform a diagnostic assessment before submitting any claims? Do you need to ship the defective product back to the manufacturer – and if so, will they cover those shipping costs?

You won't always find answers to the questions above in warranty documents. In the following sections, we detail key differences between battery warranties for your convenience. Your installer can also be an invaluable resource for the inside scoop on warranty claims.

How do battery warranties compare between some of the most popular brands? Below, we evaluate the warranties of the Tesla Powerwall, the LG Chem RESU 10H, and the Sonnen eco 10.

Telsa Powerwall

The Telsa Powerwall is a lithium-ion battery. Tesla offers a warranty term for a set amount of years (10), a throughput warranty, and an end-of-warranty capacity guarantee for this product. Notably, the Tesla Powerwall 2 includes a built-in battery inverter, and their warranty covers both the battery and the inverter. 

LG Chem RESU 10H

Like the Tesla Powerwall 2, the LG Chem RESU 10H is a lithium-ion battery. LG Chem also offers the same warranty term as Tesla (10 years) but provides a smaller throughput warranty. Some of this difference could be attributed to the size variations between the two technologies (8.8 kWh usable capacity for LG Chem vs. 13.5 kWh for the Powerwall).

The LG Chem RESU 10H is solely a battery unit and, therefore, requires a separate inverter component to operate. This battery is often paired with SolarEdge's StorEdge, a battery-ready inverter with a 10-year warranty.

Sonnen eco 10

Unlike the other two options above, the Sonnen eco storage system includes lithium-iron-phosphate (LFP) batteries. Lithium-iron technologies are newer to the solar market than most types of lithium-ion batteries and lead-acid batteries, but they often boast longer lifespans and more cycles than alternative chemistries.

Unlike the Tesla Powerwall 2 or the LG Chem RESU 10H, Sonnen's warranty doesn't guarantee a specific throughput rate; the warranty lasts for ten years or 10,000 cycles (whichever comes first). Sonnen does provide estimates for throughput based on cycle count in their warranty agreement: an eco 10 (4 battery modules) has a throughput estimate of 58 MWh, surpassing the energy throughput of the Tesla Powerwall 2 despite having a smaller usable capacity (10 kWh).

The key to finding the right solar-plus-storage system for your home is comparing multiple quotes from solar installers. Register on the EnergySage Marketplace for up to seven competing quotes from local installers. If you prefer one type of battery over another, simply note it in your account when you sign up so installers can quote you accordingly.