Energy Products

Will Backup mode have adverse effect on longevity of batteries?

edited November -1 in Energy Products
My Powerwall was installed yesterday. It came with 18% charge and today my 12 years old 5kW pv system charged it to 98% in backup mode. I live in the SF bay area and lately with the long power outages by our terrible utility company PG&E it will be nice to leave it in the fully charged state for the next black out but I wonder if that would be bad for the battery pack. For my Tesla car it is advised to not leave the car charged at 100% for a prolonged time. Secondly my app will not let me lower the battery reserve. I guess I'll call Tesla for help regarding that issue. Any ideas will be appreciated. Thank you.


  • edited November -1
    You will be able to customize in a few days. We weren’t able to right when we got them.
  • edited November -1
    Thanks @lilbean. I see you on the Model 3 forum all the time. Do you have a non Tesla Solar system? I was wondering what you can control from your Powerwall app. Thanks.
  • edited November -1
    Hi, @nvjx! You’re welcome. We have a non Tesla solar system that was installed ten years ago. We just had two powerwalls installed.

    In a few days, a “customize” choice will be available. Here you will be able to: choose backup only, which will keep the battery at 100%; self-powered, where you can choose the reserve level for outages; advanced, to choose the level if you want it to vary for time of use; and you can toggle storm watch on and off. (Storm watch sets it to backup only.)
  • edited November -1
    Thanks @lilbean. This morning the customize choice appeared however the time of use is not available yet - maybe in another day or so. So far I am leaving it in backup mode with 98% charge. Do you think leaving it in that high SOC will affect the battery adversely? Thanks.
  • edited November 2019
    That is a good question. I don't have an answer to that. From what I've read, it's a different technology than the car batteries so hopefully that doesn't adversely affect the batteries.
  • edited November -1
    We installed 2-PW2's 16 months ago to complement our 7 year old 13.2 kWh PV system, and we operate our PW2's in self powered mode with backup set at 25 percent to cover potential brownouts/blackouts. This has worked well for us up in Edmonds, WA where we do not get many brownouts/blackouts. Using this apporach we are operating as a microgrid for ~9 months of the year with zero grid draws. We do rely on the grid to supplement our solar from November-mid-February. In self-powered mode you can set the battery backup at any level. Can't comment about your question about whether leaving the PW2's at 100 percent degrades the longevity of the battery, but I agree with @lilbean that it probably does not adversely affect the batteries to leave in high SOC..
  • bpbp
    edited November -1
    Tesla must have addressed this issue for battery storage products - since the Megapack used by utilities could have packs sitting at 100% for extended periods - ready to provide power to the grid when needed.

    Tesla lists the total capacity for a PowerWall is 14 KWh - while the usable capacity is 13.5 KWh. By not using the extra .5 KWh, Tesla could be using that extra capacity to avoid charging to 100% or discharging to 0%.
  • edited November 2019
    @lilbean- how was your process to get and have PW installed? How long did it take from time of application to install?
  • edited November 2019
    Thanks, everyone. I did notice that my powerwall charged to 98% max in backup mode and stayed there. @Tesla-David here in No California backup power is of primary concern because of blackouts. The week before our Powerwall was installed we didn't have power for over 31/2 days. It felt like going back to medieval age. I wanted 2 Powerwalls but the salesman told me it would delay installation so I went with one. I am going to leave it at 98% until the threat of blackouts subsides and then adjust it down a bit.
  • edited November 2019
    Hmmm. I applied for the Powerwall when it first came out and then got a response a year later saying that I will get it the 9 months. Then Powerwall 2 came out and applied for that, put money down and waited I think about a year. I pretty much gave up thinking it was never going to happen. Then I finally got an email questionnaire and submitted pictures. It took about three months after that to finally schedule the installation. My panel had to be upgrade and our solar was disconnected for a month! The city was slow to approve the installation. We finally got two powerwalls installed a month ago. It was a brutally long wait watching others on the forum get theirs and hearing nothing. Glad it’s finally in just in time for the corrupt power companies who cut our power off.
  • edited December 2019
    I have also wondered about leaving the Powerwalls at a high SOC. Just the experience with Tesla and lithium batteries tells us that best long term battery health is achieved by generally staying between 50% to 80% as much as possible.

    I rarely charge our Tesla above 80% unless I know I am going on a long trip. My regular driving simply doesn't require ever having the Tesla at 90% or above.

    So we just got the solar (16 kW) and two Powerwall 2 units installed last month. I don't see an option to set a maximum charge level on the Powerwall system. If so, I would stop at 80%, but I cannot, so it charges to 97% or 98% usually.

    I have been playing around with the Self-powered percentage to use. My solar system is big enough that it can fully recharge both PWs by noon to 1pm, even if it starts sunrise at 5% on a partly cloudy day.

    Then when the sun goes down (around 5:30 pm right now), the discharge begins.

    So I figure that by setting my system to be Self-powered at 10%, then I am mostly recharged every day. I am only spending about 5 or 6 hours at max SOC. The most I have ever seen it at is 98%.

    So my battery packs are spending about 18 hours per day at something less than max SOC.

    So what is the trade-off?

    Do you want the regular cycles put on the battery pack, but also avoid being at max SOC most of the time?

    Or is it better long term to just leave it as max SOC full time and dump 100% of the extra solar energy to the grid?

    I have made the decision to use the battery pack in Self-powered mode daily. It let's me have a good idea how much I can rely upon the battery pack in a true outage situation. It helps me understand what needs to be turned off to make it through the night until the sun rises the next morning.

    The system has a warranty for 10 years with unlimited number of cycles. So use it. I figure in a few years I will likely add another Powerwall to the system to makeup for any losses due to age or use. I just hope Powerwall 3 can be added on to a system that already has Powerwall 2.
  • edited July 5
    I was into this iss ue and tired to tinker around to check if its possible but couldnt get it done. Now that i have seen the way you did it, thanks guys
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