ATMEGA AVcc pin - low pass filter
The filter is only needed if low noise is important to your application.
For monitoring batteries, you probably don't need the accuracy level at
which you would want the filter. For what it's worth, the Arduino Uno
doesn't have such filter: it's AVCC is connected straight to VCC.

If you really want the filter, the exact characteristics are not
critical. The datasheet suggests 10&nbsp;µH + 100&nbsp;nF, so this
should be a safe choice.



Edit: To answer the question in the comment, yes, it is generally
advised to use decoupling capacitors, usually something like
100&nbsp;nF, even when powered from a voltage regulator.

Notice that both the VCC and the AVCC pins are very close to a ground
pin. Best practice is to use one decoupling cap for each (A)VCC/GND
pair, and to place that cap as close as possible to the pins.