We have multiple batteries (2 from 2012, 1 from 2011, and various from previous years) each battery works perfectly except 1 of the ones from 2012.
When we use the AndyMark provided via FIRST Choice, everything connect great but then the robot loses communication after running the robot for 1 second. Also it seems like the max voltage it gives is 12V while the others when full charge are closer to 13.25V.
Is this the sign of a bad battery?
Maybe.
There are 2 things you need to worry about: State of Charge (SoC) and Capacity.
Measure SoC with a voltmeter after the battery has been resting (off the charger) for an hour or two. 12.65 volts is 100%, 12.4 is 75%. Remember your voltmeter’s accuracy here.
Measure Capacity by loading a fully-charged battery with a 1 Ohm resistor* and measuring the battery voltage at exactly 15 seconds of load. You’ll see voltages well below 12.4 volts, just compare all your batteries. (Note this is not the “ideal” way to measure capacity, but it is sufficient)
*Rated at not less than 15 Watts. We used a ~100 foot spool of #14 wire for this purpose. Anything from 1.5 to 0.7 Ohms is OK, remember you just want to compare.