@bri96978 that "replace spark plugs and adapters for them" is not what "Kills" your battery. Use your voltmeter and check the output of your alternator. Then check the voltage on your battery connections with the engine running. Let us know what voltage you get. Check your wiring. Make sure that you have good ground. Your vehicle is a bit older so you need to check the wiring harness,for corrosion on all connections.Let us also know what engine size your Ranger is.
Check your battery for parasitic voltage draw. Remove the ground cable from the battery. Take your voltmeter and change it to Amperage (10A will be okay) Now take the leads from your meter and connect them in series between the battery cable and the negative post of your battery. Now make sure you close the doors etc. so that all courtesy lights are off etc. Give it about an hour or so and then check what the Amp meter shows. It is okay to use a few mA to keep the "computers" etc. alive. If the mA are to high, keep the meter connected and pull the individual fuses. The fuse that drops the mA when pulled, is the circuit that gives you the issue.
Check something like this video for some idea on how to check it. Not your vehicle make or model, just an idea for visual.