Wrong voltage measured with a DAQ in presence of a RC filter
The input impedance is indeed 144 kΩ:

\begin{equation}
R_{in} = 127 k\Omega + (30.9 k\Omega || 39.2 k\Omega) = 127k\Omega + \frac{(30.9)(39.2)}{30.9 + 39.2} k\Omega \approx 144.28k\Omega
\end{equation}

Hence, in steady-state (capacitor is an open circuit), your RC filter creates a voltage divider with the input impedance of the analog front end. If you are measuring in differential mode, the input impedance is doubled, at approximately 289 kΩ, which explains your reading of 1.22V (battery voltage was about 1.46V).

The 30.9kΩ and 39.2kΩ create a voltage divider with the 2.5V reference, effectively biasing the measurement to 1.398V (for use with a single supply instead of traditional bipolar supplies).