I’ve got a 98 ranger and they battery keeps dying. The battery is only 3 months old and has a brand new alternator. I’m not sure what to do or try. Any suggestions would be helpful.

 

Welcome to the forum

Get out the volt meter
Open the hood
Test battery voltage, 12.3v to 12.8volt is acceptable
12.8v newer battery
12.5v is 3 year old battery
12.3v is 5/6 year old battery and time to watch for battery sales

12.2v or less is a failed or drained battery

On back of alternator is the B+ terminal, stud and nut, test its voltage, use alternators metal case as the ground
Should see BATTERY VOLTAGE exactly as you just tested
If not then fuse or fusible link is bad

Unplug 3 wire connector on alternator, yellow, green and white wire
Test Yellow wire, should see battery volts exactly, if not then fuse is blown

Test green wire, should be 0volts
Turn key ON
Retest green wire, should now be battery volts, can be .1v less

If all 3 wires check out then Trucks side of charging system is OK, 100%, all good, for sure

Start engine
Test battery voltage again
Should now be above 14volts, 14.2 to 14.8volts
If under 13.5volts then new alternator is bad, for sure, doesn't matter if store says "it tests good" it ain't, for sure

Let engine idle for 5 or more minutes
retest battery voltage, should now be under 14volts, alternator is working
If still over 14v wait another 5 min and retest

If that all checks out, turn off engine
Unhook 1 battery cable, doesn't matter which one
Let it sit for an hour and test battery voltage, WRITE IT DOWN
Wait another hour(or more) and test again, if its lower then your New battery is bad, self draining, it happens, same as bad new alternators

If voltage is the same then vehicle has a circuit that is draining the battery when key is off
You will need to use an AMP gauge and pull 1 fuse at a time to find that drain