Add battery to existing SunRun installation?

So we screwed up when initially planning our system 3 years ago – should have got 3 batteries instead of 2. (13.02kw system with 2 Tesla power wall 2s, 39 panels)

System was completely designed, installed by SunRun (was actually the best option if the available).

Get SunRun to come back out for a ‘sales’ call to see about adding an additional battery to my system.

Rep says that they can’t do it and I need at least 7 panels for a 2.6Kw system to add the additional battery. Cost ~$28K before rebates. Any way rep states that they can’t do it because of some technological thing they haven’t figured out or some other BS. I don’t need the panels, just want the battery as my system will easily support a 3rd.

I know they are saying BS as a way to make a lot more $$ of the panels/install as they margin is probably much higher with panels then batteries.

I reached out to Tesla directly and am probably going to go through them (~$9K before rebates/credits) for just the battery.

Will any of that void my warranty with SunRun? What I see potentially happening is the 3 battery is stacked with the other two, the.wired into the Tesla gateway with its own breaker, and the gateway configured to recognize the 3rd battery. (See my logic in calling SunRun’s BS.)

I own the system outright, so no lease or PPA issues.