I have. I own both a homebrew battery system and am also a StromTank dealer, as well as a Synergistic Research dealer.
I started out with just a line conditioner on a dedicated line for a number of years, and I had progressed to the PowerCell SX before considering a battery system. I followed one thread on here that talks about creating a battery system and did the same, using two LifePo4 batteries and a Giandel inverter. The improvement was significant in terms of focus, imaging, and soundstage.
I upgraded to the PowerCell 14 as it came out in July, and the improvement continued with regards to soundstaging, image delineation, and straight out dynamics as they are now also designed as supercapacitors that deliver more instantaneous current than the wall can provide. The difference of having a battery system became smaller, but the benefits were still audible.
I recently became a Stromtank dealer and have a few units on my floor, which replaced the homebrew design. I didn’t think I would hear any improvement, but I was surprised when I did. I learned that the inverter in the StromTank operates with a much lower noise floor than a typical Giandel inverter.
So now, I have a PowerCell 14 hooked up to a StromTank battery supply. Maby audio enthusiasts likely wouldn’t think to or have the financial means to prioritize having both a battery supply and quality conditioner working together in the chain, but doing so will elevate your total system performance to new heights you would have otherwise not dreamed.