Hey Jerry,
Great comments.
Yes, the StromTank converts the energy stored by its LFP4 batteries via inverter back to AC. The rated THD per their website is “<2%”. While that is greater than PS Audio’s <0.5% (0.1% is not guaranteed), I can easily say that in my experience, PS Audio products are sonically inferior to the StromTank and Synergistic Research PowerCells… and by a large margin.
In my experience, I’ve found that not everything that is measurable is audible, and not everything that can be heard is measurable. While the inverter itself may remove distortion, there’s no telling what is happening after that stage, how electromagnetic activity after the inverter, how much instantaneous current is being delivered, etc. I owned PS Audio regenerators prior to switching to SR, and have also extensively demoed the P20 against the PowerCell SX a few generations ago and found the PowerCell to be far superior in performance with regards to dynamics, imaging, staging, and natural timbre/tone. This was well before the time that I became a dealer by trade, and I was a PS Audio fanboy prior who was very active on their forums. The PowerCell has since gone through many improvements that make it even significantly better than it was then, and the P20 has not changed a bit. And this is all considering that the PowerCell does not have batteries contained in them.
I’ve found that PS Audio PowerPlants are good with source devices, but amps don’t do so well on them. Many other PowerPlant owners have also preferred to plug their amps directly into the wall instead. The PS Audio forums now have threads that talk about power products that their customer base are now raving about that trump their P20s.
Regarding the isolation of the charger in a StromTank, I will have to ask the StromTank team. I do know there is a button to completely turn off the charging and access to the grid, but I don’t know what the circuitry entails.
When I was using my homebrew solution, the Giandel inverter generated around 3% THD, and I had a connector that I could disconnect to easily remove the charger from the chain.