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Powerwall Full Drain Damage

Does leaving a Powerwall on at 0% charge for many weeks damage it?


  • Total voters
    15

hawkman

New Member
Apr 30, 2018
3
0
SoCal
Hello,

I just had my Tesla Solar + Powerwall system turned on here in SoCal, after an absolutely horrendous series of mishaps along the way (began purchase process in August of 2017 for activation in December 2017, so you can imagine how many delays and mess ups there were, being 4 months behind schedule.

When they came to boot on the system last week the Tesla rep was shocked to see that the 2 Powerwalls were already on, and had been sitting at a 0% charge state for what I calculate to be nearly the past 2 months.

I have a conference call scheduled with them about it, for what I expect to be a series of explanations trying to convince me that no damage has been done.

What empricial evidence can I gather or request from them to evaluate and verify the health of my Powerwalls? Have they likely lost some % of their effective full capacity?

I am very disappointed in my experienc with Tesla so far, and if I had a time machine I would never embark on this journey again. Unfortunately, I am already here....
 

hawkman

New Member
Apr 30, 2018
3
0
SoCal
The Powerwalls have a 10 year warranty and are guaranteed to have 70% of the original 13.5kWh capacity through the warranty period. They (and you) should be able to run the Powerwall from 100% to 0% and show the amount of energy that came out. It should be evident from that whether the batteries are damaged or not.

I believe my contract states that the Powerwalls should have 85% of their original capacity remaining after 10 years, but I have to doublecheck. The thing I don't want happening is a) my original full capacity amount begins diminished because of the mistake by the installers, or after 10 years I would have 90% remaining but instead I end up with 86% remaining, still within spec and not claimable under warranty but also less than it should have been.

Also, they set the Powerwalls with a reserve amount of 40% at present, so it doesn't go down below that. Also, my Tesla app doesn't have very granular details so that I can determine full discharge amounts (I think), and it's made harder to measure that due to solar and grid both being in play throughout the day/night. I appreciat the idea - maybe I can run the house on full powerwalls somehow and do what you advised. I haven't figured out how to do that just yet.
 
My provisioning took about 2 months also and I asked about the battery draining, as they were losing about 1% a day over October. They just said to turn off the powerwalls. I turned them back on and they had the same % that I turned them off with.

As mentioned, the warranty guarantees at least 70% for 10 years. The app shows about 3% higher than it really is, but if they were sitting for 2 months without charging but while on, then yea they probably went to zero, unless there is some internal mechanism to shut it off.

I would try fully charging and see if you get the full charge amount for both of your powerwalls (13.2 kWh per powerwall, I believe). If it gets really close to that, you should be fine. Tesla has been very proactive for me on my system. I had one of the Neurio sensors flipped and they came out and fixed it without me having to call them.
 
Two of the stats that the powerwalls track are the imported and exported energy from the battery. If you have access to the system on your local network, you can get this information in a browser (at IP address/api/meters/aggregates). Having said that, I'm not sure it's clear exactly how much energy you would expect to come out of a full battery cycle. It's possible there are reserves that are not user-visible to preserve battery health.

The information is in JSON format. Here's an example from my system:

Code:
{{  
   "site":{  
      "last_communication_time":"2018-04-30T15:25:47.187412774-07:00",
      "instant_power":-4359.0400390625,
      "instant_reactive_power":-846.239990234375,
      "instant_apparent_power":4440.4225230513675,
      "frequency":60,
      "energy_exported":1157919.6177829541,
      "energy_imported":1343670.0336162874,
      "instant_average_voltage":257.1999969482422,
      "instant_total_current":0,
      "i_a_current":0,
      "i_b_current":0,
      "i_c_current":0
   },
   "battery":{  
      "last_communication_time":"2018-04-30T15:25:47.189407753-07:00",
      "instant_power":-10,
      "instant_reactive_power":900,
      "instant_apparent_power":900.0555538409837,
      "frequency":59.987,
      "energy_exported":167510,
      "energy_imported":247130,
      "instant_average_voltage":256.8,
      "instant_total_current":-0.4,
      "i_a_current":0,
      "i_b_current":0,
      "i_c_current":0
   },
   "load":{  
      "last_communication_time":"2018-04-30T15:25:47.186927113-07:00",
      "instant_power":816.2839872584973,
      "instant_reactive_power":119.3805168957203,
      "instant_apparent_power":824.9674270351042,
      "frequency":60,
      "energy_exported":0,
      "energy_imported":2203166.4219444445,
      "instant_average_voltage":257.1999969482422,
      "instant_total_current":3.1737324920060663,
      "i_a_current":0,
      "i_b_current":0,
      "i_c_current":0
   },
   "solar":{  
      "last_communication_time":"2018-04-30T15:25:47.186927113-07:00",
      "instant_power":5190.639892578125,
      "instant_reactive_power":66.7299976348877,
      "instant_apparent_power":5191.0688096968815,
      "frequency":60,
      "energy_exported":2097377.8614049847,
      "energy_imported":341.8552938734316,
      "instant_average_voltage":257.1699981689453,
      "instant_total_current":0,
      "i_a_current":0,
      "i_b_current":0,
      "i_c_current":0
   },
   "busway":{  
      "last_communication_time":"0001-01-01T00:00:00Z",
      "instant_power":0,
      "instant_reactive_power":0,
      "instant_apparent_power":0,
      "frequency":0,
      "energy_exported":0,
      "energy_imported":0,
      "instant_average_voltage":0,
      "instant_total_current":0,
      "i_a_current":0,
      "i_b_current":0,
      "i_c_current":0
   },
   "frequency":{  
      "last_communication_time":"0001-01-01T00:00:00Z",
      "instant_power":0,
      "instant_reactive_power":0,
      "instant_apparent_power":0,
      "frequency":0,
      "energy_exported":0,
      "energy_imported":0,
      "instant_average_voltage":0,
      "instant_total_current":0,
      "i_a_current":0,
      "i_b_current":0,
      "i_c_current":0
   },
   "generator":{  
      "last_communication_time":"0001-01-01T00:00:00Z",
      "instant_power":0,
      "instant_reactive_power":0,
      "instant_apparent_power":0,
      "frequency":0,
      "energy_exported":0,
      "energy_imported":0,
      "instant_average_voltage":0,
      "instant_total_current":0,
      "i_a_current":0,
      "i_b_current":0,
      "i_c_current":0
   }
}
 

miimura

Well-Known Member
Aug 21, 2013
7,398
7,400
Los Altos, CA
If you want to measure the Powerwall energy available, reduce the Reserve to 0%, wait for it to charge fully from solar, then turn off the breakers for the solar and the grid. The house will run completely from the Powerwall and the app will show how much energy came out. Below, you can see the "From Powerwall" figure for the time period shown. If you scroll below the chart there is a "To Powerwall" figure also.

2018-04-30_15-29-46_000.jpg
 
Last edited:
  • Informative
Reactions: pilotSteve

bkp_duke

Well-Known Member
May 15, 2016
8,187
41,631
San Diego, CA
Powerwalls have about a 5% reserve. I know from experience with our three. You CANNOT see this reserve on the app, but if you monitor your powerwalls directly via the IP you can see it. It's not commonly known, but watch the % on your app vs. a web browser on your local network. At 100% they match perfectly, and then as the PWs discharge, they diverge until they hit the reserve.

So even if they went down to 0% on the app, they were likely at 5% in reality as the system is smart enough to keep that reserve and not let you touch it so as to not damage the system.
 
Recent battery experience in the industry is at least 10+ years old by now. There is no way you can actually hit 0% (internally) on the PW just as you can't hit 0% on any BEV vehicle (except maybe the first-gen Leaf). They already know the best long-life usage range for batteries is between 80% and 40%. The end-points are guarded off to avoid damage.

It's 14+ kWh after-all, and we only get to see less than 13.5 kWh of it.
 

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