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PylonTech, Powervault, Powerwall 2... What's In the Warranty?

Erica Charles 12 Jun 2018

Following our analysis of Powervault 3 vs Powerwall 2, we had a couple of requests for a review of the SoFar / Pylontech residential battery storage system.

On the face of it, the SoFar / Pylontech combination offers good value, flexible sizing, and LFP (Lithium Ferro Phosphate) chemistry… so well worth consideration.

And that's before you appreciate the fun to be had when trying to summarise the essence of the different warranties: Pylontech vs Powerwall vs Powervault.

Here goes…

System Overview

The SoFar / Pylontech ‘system’ is an ac-coupled storage system combining SoFar’s 3kW inverter / charger with the Pylontech 2.4kWh (90% usable capacity) US2000B Plus LFP battery module. 

It is not actually an integrated 'system' – the installer basically combines a battery with a compatible inverter / charger, both of which are separate units from separate manufacturers with separate warranties.

It is possible to combine one inverter / charger with up to eight US2000B Plus batteries, giving a nominal battery capacity of between 2.4kWh and 18.2kWh. The system closest in size to Powerwall 2 would use 6 batteries, giving a usable capacity of 13kWh, whilst the system closest to Powervault 3 would use 3 batteries, giving a usable capacity of 8.6kWh.

Specifications are as follows:



Powervault 3

Tesla Powerwall 2

SoFar / Pylontech 9.6kWh

SoFar / Pylontech 14.4kWh

System type:

All-in-one unit

All-in-one unit

Separate Charger +Stack of 4 Battery Units

Separate Charger +Stack of 6 Battery Units

Usable capacity:









Charger rating (maximum power input):


3.68kW or 5kW subject to grid permission


Continuous power output:


3.68kW or 5kW subject to grid permission


Round trip efficiency:



Max 88%


Online portal

Tesla App



Wall or floor mounted

Wall or floor mounted

Wall mounted inverter

Indoors / outdoors:

Indoors only

Indoors or outdoors



10 years

10 years

Battery: 10 years, Inverter / Charger 5 years (extension to 10 / 20 years available)



The rough installed system costs, including VAT at 5% (i.e. if installed with solar) are as follows:



Powervault 3

Tesla Powerwall 2

SoFar / Pylontech 9.6kWh

SoFar / Pylontech 14.4kWh

Approx installed cost incl VAT @ 5%





Usable capacity:





Cost / kWh usable capacity:






Powerwall 2 wins on absolute cost per kWh of capacity installed, with the similarly sized SoFar / Pylontech system a close second.

But Pylontech is an LFP (Lithium Ferro Phosphate) battery, as compared with NMC (Lithiated Nickel Manganese Cobalt Oxide), used by Tesla Powerwall 2.

So in theory at least you would expect to get much more lifetime output from your Pylontech system than you would from your Powerwall system.

Or would you?  Prepare to be 'mind-boggled' by the finer points of battery warranties...

“Reasonably Expected” Output


First, look at what might reasonably be expected from the three systems:

  • The Pylontech datasheet (US2000B Plus) says that the batteries will provide storage capacity of more than 4,500 lifecycles at 90% depth-of-discharge.
  • So for the 4 battery Pylontech system, the ‘datasheet’ expected output is 38,880kWh compared to an expected output of 51,800 kWh from the equivalently sized Powervault 3 system (also LFP).
  • For a 6 battery Pylontech system, the ‘datasheet’ implies an expected output of 58,320kWh. This compares to an expected storage capacity of 47,800kWh for the equivalently sized Powerwall 2 system (37,800kWh guaranteed, expect another 1000 lifecycles at 80% End of Warranty capacity).

So on the face of it, it looks as if the cost per kWh 'storage slot' is around 13.3p per kWh for the 9.6kWh SoFar / Pylon system, compared to 14.8p /kWh for Powervault 3. 

And 12.1p per kWh for the 14.4kWh SoFar / Pylontech system, compared to around 13.4p per kWh for Tesla’s Powerwall 2.

Thus on the basis of lifetime cost per kWh stored, SoFar / Pylontech appears to win…

But now read the actual warranties and you find that the battery offering the best warranty, by a country mile, is Powerwall 2 (subject of course to no more April Fool tweets from Elon Musk….):

Pylontech Warranty

The Pylontech datasheet may imply an expectation of more than 4,500 lifecycles, but the actual warranty doesn’t mention life cycles or guaranteed minimum output. In fact it’s quite hard to decipher exactly what it is guaranteeing. As far as I can see it says:

  •  “Pylontech warrants that the Product will be free of defects caused by improper workmanship or defective materials”, with a condition that “the product must be used on a daily cycle basis and only for energy storage system.”
  • This warranty commences the period of Seven (7) years from the earlier of: 1. the date of installation of the Product; or 2. six (6) months after the date the Product was manufactured.
  • But then there’s this line: “Pylontech may require You to complete root analysis testing of the Product to provide evidence supporting the claim. Final verification of the claim will be made by Pylontech”.

[Good luck with your “root analysis”.  The term is not defined. Whilst it’s reasonable to assume you won’t be sending the system off to the Royal Horticultural Society along with a sample from your neighbour’s tree, it’s anybody's guess what exactly you should be doing ….]

  • One term that is defined is "Minimum Capacity". The definition is as follows:

“Minimum Capacity means at least 70% of the Nominal Energy during the Warranty Period.”

So far so good. Except that the term is only used twice, as follows:

  1.  “Warranty period could be extended to Ten (10) years FOR FREE by successfully register your product on Pylontech website: ,and the Minimum Capacity/remaining capacity in this document would be not less than 60% of the Nominal Capacity at the end of Warranty Period.”
  2. In order to claim under this Warranty, You must: 1. present the certificate of warranty declaration in its original form; 2. submit the invoice for the procurement of the Product indicating the date of delivery; and 3. provide the Pylontech system log data recorded by the Product as an indication of whether or not the Minimum Capacity has been achieved (but this would not be determative).
  •   In summary therefore it looks as if to claim, you would need at least to prove that the battery capacity had fallen below 70% of nominal during the warranty period (7 years) or 60% (10 years), but that may not be enough (‘determative’ – their typo, not mine). In addition you may need to do root analysis testing at your expense, but who knows what that means.
  •  And then perhaps the most difficult thing at all, to claim you would need to contact

 Address: No. 73, Lane 887, ZuChongzhi Road, Zhangjiang Hi-Tech Park, Pudong, Shanghai; Post Code: 201203 Telephone +86 2151317693 / +86 2151317697 Fax: +86 21-51317698 Email:

Tesla Powerwall 2 Warranty

Tesla guarantees the Powerwall 2 will be free from defects for 10 years, will have an initial capacity of 13.5kWh at installation, and at 10 years will retain 80% of its capacity, subject to a limit of 37,800kWh throughput if the battery is used for more than storage of excess solar and / or back-up.

Note the UK telephone number on page 5, the presence of a UK support team, and, by the way, installation audits carried out regularly by Tesla.

Powervault 3 Warranty

Since our initial Powervault 3 vs Powerwall 2 analysis, we’ve spotted this document on Powervault’s website, relating to the warranty of Powervault 3.

As with the Pylontech warranty, it’s a bit mind-boggling, but for different reasons.


The Powervault 3 7.5kWh datasheet shows a 10 year warranty period and an “MWh under warranty” of 51.8MWh. There is something called a “Degradation at End of Warranty” of 70%.

But now look at the fine print of the warranty:


  • Paragraph 3 [or just below it] “Powervault warrants that the product will be free from defects in materials and workmanship for Warranty Period. If the product proves defective during this Warranty Period, Powervault, at its option, will either repair the defective product without charge for parts and labour, or will provide a replacement in exchange for the defective product. The customer will cover the cost of shipping replacement parts.”

 [Bit ‘ouch’ that you have to pay for shipping for your replacement parts, but the real issue is ‘what does defective mean?’…].


  • Paragraph 5 [I’ve taken the key phrases] If the battery capacity drops below the End State of Health before the battery has delivered the MWh Throughput; and before the Warranty Period has expired, Powervault will supply a replacement battery at a pro rata cost calculated as follows:
  • Powervault will confirm the replacement battery list price (“ReplacementListPrice”) and the MWh rating of the closest new battery “New MWh Throughput” at the date of the replacement.
  • Powervault will provide a discount to the customer equivalent to the MWh not provided under the initially warranted battery. The customer will pay Powervault according to the formula

ReplacementListPrice x (1-((MWHDelivered  ÷ New MWhThroughput)/New MWh Throughput) and Powervault will provide a battery replacement.

[Help. Really feeling like I am back in an A level maths exam at this point.

Let’s say after 7 years I think my system has failed such that it’s outputting down to 60% of capacity (below the 70%). So far it’s provided me with 300 days x 7 years x 7.5kWh = 15.75 MWh.

To my mind the product would then be defective so as a consumer I might expect to be able to get a replacement under Paragraph 3 if I am happy to pay the shipping cost. But where do I sit under Paragraph 5? Looks like I may have to buy a replacement!

Let’s say the Powervault range hasn’t moved on at this point and the replacement is the same as the original. Now try and apply the formula.

Oops, I don’t think you can – the brackets are wrong….. There are three opening brackets, and only two closing brackets. 

I tried it on Mauricio in our office. With the confidence of youth on his side, Mauricio decided to ignore the missing bracket. He also couldn't read the ' ÷' sign as it's not clear in the original, and so he applied the formula like this:


Customer pays:

Replacement List Price x [1 -

(MWh Delivered – New MWh Throughput)




New MWh Throughput



In my example MWh delivered = 16MWh and, if the replacement is similar to the original, New MWh Throughput  = 52MWh.

Plug these numbers into Mauricio's version of the formula, and the Customer is expected to pay 1.7 x the battery replacement cost! Which would seem to add insult to injury when you haven’t had value out of the original.

So we checked with Powervault and they said the formula in brackets should be:

(1-((MWHDelivered ÷ New MWhThroughput)/New MWh Throughput))

At which point it's starting to look like something we should try on the Secretary of State for Education on Breakfast Time TV to see if he can apply primary school BIDMAS rules under the pressure of the cameras.....

Anyway, plug my numbers in the brackets you get

1 - ((16 MWh/52MWh)/52MWh)

Which is technically not able to be calculated since the units in brackets aren't consistent. But comes to 99% if you ignore the units.

So you pay 99% of the Replacement Cost?

We are still scratching our heads. Is it April 1st today?]


On the face of it, SoFar / Pylontech offers a lower ‘lifetime cost per kWh stored’ than Tesla’s Powerwall 2. 

But realising the value is dependent on the product delivering the 4,500 cycles @ 90% depth-of-discharge, as stated on the datasheet. 

With daily cycling, 4,500 cycles are going to last just over 12 years. The Pylontech product warranty can be extended to 10 years, but it in no way backs up the expectation of the 4,500 cycles statement. Claiming on the warranty does not look straightforward. 

[And that’s before we even consider the warranty of the SoFar inverter / charger.. at least with Powerwall 2 and Powervault 3, one warranty covers both parts of the system].

As we repeatedly conclude, despite looking at many other residential solar storage systems, Tesla’s Powerwall 2 seems to win hands down – simple design, beautiful aesthetics, on-the-ground support in the UK, and a strong warranty ... which is a positive joy to read when you are faced with the competitor warranties!


Topics: Solar PV battery storage, Tesla Solar Battery, Powervault 3, Pylontech

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