Battery died a few weeks back so I replaced the battery and the terminals thinking the old battery was week. But after it sat for a about a week it was completely dead. Nothing plugged in the 12 volt or anything? Is there a known issue for these or is it a wild goose chase to find the culprit? 1999 4l V6 supercab ranger

 

No, no known issues

Best bet is to first unhook either battery cable, test battery voltage and write it down, and let it sit for a few days, and then retest battery voltage
If voltage has dropped battery is self draining, it happens to new and old batteries, internal short
If voltage is the same then you can test for a drain from vehicle

You need an amp meter, connected between battery terminal and and its cable, KEY OFF and in your pocket

Expected amp draw is 0.03 to 0.07 amps(30-70milliamps), from computer memory, radio clock/preset memory, PATS(1999 and up) and "keyless entry" if so equipped

If amp draw is higher then unplug Fuse 25 in cab fuse box, this puts GEM module to sleep, it stays on for 20 to 30min after door is closed then times out
See what amp draw is now
If still high look at the diagrams and start unplugging fuses that have 12volts ALL THE TIME not ignition switch ON fuses, its possible the ignition switch is leaving a circuit ON but not likely