This is true. I have the ST-300 running on battery power and leave audio cables permanently plugged into input and output. The battery lasts for ages, I think I've changed it maybe 2 or 3 times in three years, and even when it does run down it gives a very clear low battery warning but keeps on working for plenty of time after that (so you wouldn't need to rush to change the battery mid-gig).I've been thinking about the ST-300 Turbo Tuner and using a 9v battery in it. I read that when it's in bypass there is no draw from the 9v
I don't notice any change to my bass tone with the tuner in bypass, and it doesn't pop when I turn it on or off.
Also of course the actual tuning function is very, very good, senses the note very fast, handles low B or A no problem on my five-string.