Hello, Mix4fix.
I did a quick search and found this:
"Includes :
1x Battery DAC board (mounted & tested)
2x NiMH Batteries (one is shown in the picture for scale, two are actually mounted inside)
Note : power supply is not included (any 12V-15V wall transformer will do, laptop supplies are ok too, car power also...)"
From this website:
https://audio.starting-point-systems.com/and on Ebay:
https://www.ebay.com/itm/201486642344Toward the bottom of the page there is a photo of the two batteries. Looks to me as though it is very simple to replace them. $215 + shipping is a GREAT price IMO.
This DAC3 reminds me of my dB Audiolabs Tranquility NOS DAC which also uses the TDA1543 chip. Mine is not battery powered however. I suspect your DAC 3 sounds sounds great. Sorry I didn't find how to change out the batteries, but (without looking at the inside) I suspect it's fairly simple to accomplish.
Michael