Battery dead after truck runs for 45 mins

have battery and alternator tested --examine wires --connectors--fuses ---dont just buy and replace parts check and test them

forget all that side show stuff
battery light (this means battery bad or Alternator dead. load test the battery fully. no way is it 19 years old and good.
charge it+ load test it(a tool) or get the battery tested in any shop or auto store, (most stores this is a free service) USA is.
then if Lamp glows again the alternator is dead.(battery good now)
caused by

• ALT is bad
• up to 3 fuses blown, for ALT.
• alt belt loose or missing?
• engine runs way way below 800 RPM, causing ALT to go off line.

last one is super rear and was EGR stuck open. super low RPM.

keep in mind, Alternators go off line on purpose if battery shorts a cell,
or has discovered an open CELL (10v battery not 12v)
this is to prevent 2 bad things, battery does not explode(acid bath)
and does not go over-voltage and blow up $3000 in electronics in the car. (never fun that and ALT's are much smarter now)

AC turns off on all modern cars for many reasons
battery lamp on,so the engine can get you home safely not wasting huge power from AC, as the ALT fails and the battery goes dead in 15 to 30 minutes, now does 30 min for sure in day light.
even DRL lamps go dead if ALT fails.LAMP battery glows.
and
to prevent evap core freeze up or compressor damage
or if engine overheats or PCM puts engine in limphome mode
to gain bad lost engine power, so you can drive safely.
The AC brain want to protect the engine and driver both.
in your mind wonder how low engine power happens passing a logging truck at 75mph.
bingo AC off line saves the day.
and at WOT too wide open throttle, drive may be in danger this.
also transmission too hot or in limphome it.
and more,

air bags brain does not like 10vdc, for DC power so , goes NUTS.
it will self cure later , new battery and or ALT

Here is my Alternator 101 class for today, what can fail. (all) Jeff nails it. (2.4 or 4.3L engine I can not guess) both are internal REG.

1. battery is bad, if shorted cell in battery , altenator shuts down to prevent battery explode and acid every where. so test the battery first, for sure over 5 years old.
2. alternator swaps and blew the 100amp fuse there , next time pull battery NEG lug to replace any ALT. or blow it again you will
3. wires bad, or unplugged or connected backwards
4. the rear ALT plug has 4 pins all 4 must be wired end to end correctly,no hack jobs seen here. and ALt lamp pin next.
5. the cluster lamp ALT must not be burned out or self excitation fails and alt is born dead. replace the ALT lamp NOw. if blowned.out. in IP cluster.
6. bad alternator or wrong one there now.(hack jobs)
7. Engine idle RPM way way below 800 RPM and the ALT goes off line then,.
8. Fan belt slip to alt. pulley, (sorry typed this out of order)
9. a battery and anD alt both can be carried in hand to autostore and they test it, better stores do that, they load test the battery and spin test the alt.
10. tests: more, put battery from good car to here and test now.
11. jumper start the car, using 2nd running car, or ask a tow truck for a jump.
12. below I pust red donuts on all fail points 3 fase MUST BE GOOD , 0 OHMS MESSURED. best is with battery unplugged never use meter DMM ohms with voltage present.(tech 101)

\
the lamp must be good as vast regulators fail , reg is inside ALT.

well IT DIED HARD what did you expect?
ok
well a tech uses an Ammeter to see if drain is excessive. 0.050A max.
or alternator is dead or super weak , easy tests. 13 to 15vdc running if not ALT IS BAD easy as pie test. Voltmeter.
or battery load tests fail./ (all auto stores do this test for free, carried in.
all repair shops can do this.
there is a reason , but only testing finds causes. GUE$$ing is not cheap.
never seen any 2004 good, ever not me. Impossible is the word.
now.

what engine size?
the PCM runs the show, and its bad. or wires bad to it.
your car has PCM regulator.
no charge battery light.?

1: takes a good battery and battery cables and lugs cleaned.
2: test the altenator, odd how 4 of yours all tested good but you replaced it 4 times, get it tested if good, its good.
3: then check that the charge .battery lamp works. if the lamp works
that means the PCM thinks that charge system is bad.
if the wires from the rear of the alt, to the battery red and Gy wires
are good all the way to PCM then the PCM is bad.
the big wire on rear of ALT , on one car had a bad lug. #6 wire.
he replaced the ALT 6 times. all wasted effort.
inspect the wiring first. that is free, and is simple fix.
and if the ALT casing is not grounded, all bets off.
same with battery minus lug not good, on BOTH ENDS>
one guy had his battery lug moved to frame, (wrong)
and this never worked.

You need to fully charge the battery and load test it, then check the charging system and alternator drive belt for tightness. do not remove cable when running or it can harm the charging system...ok on older cars, no longer good practice. Quick check of charge system can be done with volt meter across the battery. Volts should read between 13 and 14volts and not drop over time. With all lights, heater etc on volts should be better than 12.5 (usually above 13 and again, not drop with time.

if doors left open for an extended period of time interior lights will kill battery have battery tested sum auto stores can do a load test and condition check of battery while in car sum do it for free most auto stores can test alternator also but most will bench test(with alt out of vehicle)

you need to get a adapter from any auto store that can handl e load you want

Likely you did this already but check fuses in power distribution box near battery (likely two 60a fuses for alt in there). Additionally, was alternator regulator tested or was alt "full fielded" for test. (regulator failure will prevent power made at alt from reaching the battery). Also, check continuity of leads going to alternator to make sure they're OK.