2007 Mercury Monterey car wont start

What you're describing is typical of a failed charging system. Start by measuring the battery voltage. If you find 12.6 volts it is fully-charged and we'll have to look for a bad connection. If it's closer to 12.2 volts, the battery is good but discharged. Charge the battery at a slow rate, then have the charging system tested. If you find around 11 volts, the battery has a shorted cell and must be replaced.

What is the battery voltage?

12.47 is not good. It will be 12.6 volts if the battery is fully-charged. This does not, however, point to a failed charging system. The next thing is to measure the battery voltage again while a helper tries to crank the engine. It must not drop to less then 9.6 volts. Measure that right on the battery posts, not the cable clamps. If it stays above 9.6 volts, remember the value, then measure again with your meter probes right on the two cable clamps. If it's lower there, one of them has a high-resistance connection and should be cleaned and tightened. If you get the same voltage, move your meter probes down the line and repeat the test. In particular look at the smaller positive battery wire where it bolts to the under-hood fuse box, and the smaller negative wire where it bolts to the body. Those are a common source of electrical problems.

Are you using an auto-ranging meter?