Forums

Will Backup mode have adverse effect on longevity of batteries?

Will Backup mode have adverse effect on longevity of batteries?

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.

lilbean | 2 november 2019

You will be able to customize in a few days. We weren’t able to right when we got them.

nvjx | 2 november 2019

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.

lilbean | 3 november 2019

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.)

nvjx | 3 november 2019

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.

lilbean | 3 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.

Tesla-David | 3 november 2019

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..

bp | 3 november 2019

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%.

charlesj | 3 november 2019

@lilbean- how was your process to get and have PW installed? How long did it take from time of application to install?

nvjx | 3 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.

lilbean | 3 november 2019

@charlesj
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.