04 ranger battery wont start truck?

[ncsdaonex]

My dads ranger is a 2004 2.3L 4 cylinder 5 speed regular cab 2wd. If he lets his door open for around 2 or 3 minutes his battery wont start his truck. He has to jump it or pop start it. He had it checked at 2 different places and they said that the battery and alternator are fine. So what can be wrong. I dont think that is normal because my 1990 ranger i can have my lights on and listen to the radio for an hour and it still starts right up. So my questions are what can cause this and what is the voltage i should have at the battery when the truck is off and also when it is at idle. Thanks, any information would be helpful.

Also what for cranking amp battery should be in it.

 

[Fx4wannabe01]

it's a 5 year old battery. replace it. when it's getting checked, it's got full juice in it since it was just driven somewhere, so of course it'll check out good.

 

[ncsdaonex]

it's a 5 year old battery. replace it. when it's getting checked, it's got full juice in it since it was just driven somewhere, so of course it'll check out good.

so you think its the battery, is there any test i can do to prove it to my dad. i know a good battery should have a little over 13 volts so if its under it is bad. would that work or not.

 

[locovaca]

Hook a multimeter up and watch it drain with the door open.