1998 mercury

starts and stalls in a few seconds battery went bad had to replace trouble since ran fine before

Make sure there are proper connections on the battery. Loose connections can cause all sorts of problems.

Also try starting the engine with the throttle pressed just a little bit (just barely off idle). If it stays running with the throttle depressed and dies when you let back off to idle, then it is likely the Idle Air Control (IAC) Valve.

dosent matter where the throttle is dies withen 2 seconds ran great till i replaced the battery