Some info on the SD-AUD20101.

The chipset is Via Technologies, Envy VT1620A,
Datasheet at

 http://abelian.org/tmp/vt1620a.pdf

Sample rates 8k/sec to 96k/sec.

Input is stereo, unbalanced, impedance about 4.2k ohms.
Full scale at max gain is around 50mV, at minimum gain
about 2V.

The input carries a DC bias of 3.0 volts with a source impedance
of around 4.7k, which you might want to use or decouple.

Noise floor at max gain with input open circuit:

 http://abelian.org/tmp/150605a.gif

The humps in the floor move around a bit and vary from specimen
to specimen.

Cross talk between the two channels is -34dB when fed from
a high impedance source but drops to -60dB if the source has
low impedance.

Most of the cheap USB dongles use a C-Media CM106 which is
lower quality with max sample rate 48k.  One China supplier was
flogging CM106 cards pretending they were SD-AUD20101 but they
got rumbled.

I would normally recommend an isolating transformer on the
input to break any ground loop, but for battery remote operation
this may not be necessary.

--
Paul Nicholson
--