DIY Battery Tester

Hi, I'd like to build and program my own battery tester, for now just AA and AAA. I am reading an analog input pin connected to battery positive terminal with battery negative terminal connected to GND. I get solid values, e.g. when I have a battery with 1.5 V I get an analog reading of 310. So that seems good to me. I am worried that it is unsafe to connect the battery straight to the board (MEGA 2560) without an additional resistor. Is this true? If I line up a 10K Ohm in series will this be ok? Is it necessary? Or is there internal resistance in the board to prevent the short?

THANKS!

It is safe to connect a 1.5v battery to an analog input (never connect over 5V tho). It would be ok to connect a 1K in series to give you a confidence level. 10K would probably be ok to, but I would go with a 1K myself.

Sounds good, thank you! Thanks for the quick reply, too!