Similar to 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. In this article, we’ll dive into what matters in a solar battery warranty, and how some of the top solar batteries – Tesla Powerwall 2, LG Chem RESU 10H, and sonnen eco – stack up.
How to evaluate battery warranties
As you’re comparing the warranty of one battery versus another, here are some of the most important factors to consider:
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 when it comes to batteries of different chemistries: lead-acid batteries generally have a shorter lifespan than lithium-ion batteries, and therefore have shorter warranty periods. As you’re comparing battery warranties, you’ll find that many lead-acid products have warranties under 5 years, while most lithium-ion battery manufacturers offer warranties of 10 years or more.
Most homeowners taking advantage of solar-plus-storage systems charge and drain their batteries daily – this is known as a “cycle”. As an addition to guaranteeing battery life for a set amount of years, some battery 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 at all) is often dependent on the chemistry of the battery: generally, lithium-ion batteries can withstand more cycles, so should have a higher cycle count in their warranty agreements than lead-acid competitors.
However, it’s important to not evaluate battery warranties based on cycles alone; because solar batteries gradually lose their ability to hold a full charge as they age, a cycle towards 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 alongside cycles: a smaller battery that has a lifespan of 10,000 cycles may actually 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.
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). Let’s say that a battery manufacturer provides a throughput warranty of 20 MWh. This means that the warranty is valid until the battery stores and delivers 20 MWh–or 20,000 kilowatt-hours (kWh)–of energy.
Because the output from cycling your battery will diminish as the years go on, it’s difficult to estimate just how many MWh of energy is provided in your warranty based upon warrantied cycles alone. In comparison, throughput warranties are a more tangible metric, allowing you to more easily assess the value of your battery over its lifespan.
End of warranty capacity rating
In addition to providing a warranty for a set number of years, cycles, or throughput, select manufacturers also provide an end of warranty capacity rating. This guarantees that your battery will hold a certain amount of capacity over the course of the warranty. For example, LG Chem guarantees that by the end of 10 years or the warrantied throughput (whichever comes first), their 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. As you’re comparing the end of warranty capacity ratings across various batteries, higher percentages are better than lower percentage guarantees.
Batteries vs. inverters
All battery systems require an inverter to convert the direct current (DC) electricity stored in the battery into alternating current (AC) electricity for your appliances. Importantly, some battery products include a built-in inverter, and as such the warranty covers both the batteries and the inverter component. However, this is not always the case: your battery may require a separate inverter with a warranty from a different manufacturer, or your system may include a built-in inverter with a different warranty duration than the battery component. Before buying a battery, check the warranty agreement to see if it includes the inverter. If not, it’s worth asking your installer what type of inverter they recommend pairing with your warranty and comparing the warranties accordingly.
Comparing top battery warranties
So, how do battery warranties compare between some of the most popular brands? Below, we evaluate warranties of the Tesla Powerwall 2, the LG Chem RESU 10H, and the sonnen eco 10.
|Name||Tesla Powerwall 2||LG Chem RESU 10H||sonnen eco 10|
|Chemistry||Lithium-ion||Lithium-ion||Lithium iron phosphate|
|Warranty (years)||10 years||10 years||10 years|
|Warranty (cycles)||N/A||NA||10,000 cycles|
|Warranty (throughput)||37 MWh||22.4 MWh||N/A|
|End of warranty capacity||70%||60%||70%|
Telsa Powerwall 2
The Telsa Powerwall 2 is a lithium-ion battery. For this product, Tesla offers a warranty term for a set amount of years (10), a throughput warranty, and an end of warranty capacity guarantee. 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
Similar to 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; however, some of this difference could be attributed to the variations in sizes 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. However, this battery is most often paired with SolarEdge’s StorEdge, a battery-ready inverter that also has 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 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; the warranty lasts for 10 years or 10,000 cycles (whichever comes first). However, 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 energy throughput of the Tesla Powerwall 2 despite having a smaller usable capacity (10 kWh).
Choosing the best solar battery for your home or business
Warranty is certainly important, though not the only factor to consider when evaluating your solar battery options: price, performance, and durability should all be taken into account before making a decision. You can compare multiple solar battery options on EnergySage’s Buyer’s Guide. Each battery has an independent quality rating that takes all these factors and more into account. If you’re ready to start shopping for a solar-plus-storage system, register on the EnergySage Marketplace to get up to seven competing quotes from local installers.