'03 Tundra Dead Battery Problems

Experiment with either a solar-panel trickle charger, or disconnecting the battery when it will be sitting. If that solves it, he has a parasitic draw somewhere. Only a few milli-amps will kill it over a week of sitting.

One usual parasitic draw nobody thinks of is parking on a steep incline, and the tilt-switch for the trunk or hood light activates.

How about a vanity mirror in the passenger side sun visor, and he's flipping the visor down to hold the sun shade in the windshield...?

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I had the same problem with my 2000 Tundra that would sit for a week or two at a time with a battery charger on it for a couple of days after it sat for a week and then, turned it off but leave it connected.

When I tried to start it a week or two later - dead. It turns out that my battery charger had a small charge indicator light that worked even when there was no power to the battery charger by drawing power from the battery; it pulled about same power as the "door open" light. After I noticed that little light, I no longer left the battery charger attached to the battery and that solved the problem. You wouldn't think that a tiny light (LED?) would drain a battery in a couple of weeks but evidently it did.

The moral of the story is to make sure everything is off. It doesn't take much over that period of time.

Skip

The leakage should be checked using an amp meter in line with one of the battery cables and switch off and or disconnect the possible culprits these would be radio (memory Circuit); Alarm; interior lamp; alternator ect. anything that is connected to permanent battery supply When the current drops considerably the fault is found. Joe

Inside your alternator is six diodes. The purpose of the diodes is to convert A/C electricity that is produced by the alternator to D/C electricity that is used by the vehicle. The diodes act as a check valve allowing what is produced by the alternator to flow out to the battery thus charging the battery and operating other items on the vehicle. When you kill the motor and the alternator is no longer producing then the battery charge will try to flow back to the alternator. If the diodes are working properly then the charge sits on the diodes and nothing happens. However, if one or more diodes are bad then it allows the battery current to flow back to and through the alternator. If this occurs the alternator will act as a Electrical motor and slowly drain the battery. You could possibly be dealing with a diode that is in the process of breaking down thus allowing battery current to flow back through the alternator and slowing discharging the battery. Try this, unplug the alternator itself and leave the battery cables connected. If the battery maintains its charge then you have a alternator issue. If, however, the battery is discharged then start looking for something inside the cab of the truck. The number one item is the stereo. If it has a memory chip it will drain the battery over a period of time. Again leave the battery cables hooked up and disconnect the stereo....Bla Bla Bla....you get the point. Keep following this procedure until you find the culprit. Modern vehicles have countless items that use a small trickle of power to maintain settings. As we drive on a daily bases they do not become issues, however, allowed to set over a period of time they can affect items like whether a battery maintains its charge. Hope this helps....."02" YOTA.

I forgot to add do not operate the vehicle with the alternator unplugged. Once your daily activities are over unplug the alternator and allow it to sit. Again never operate the vehicle without the alternator plugged in. The reason is if the vehicle is running and you try to plug the alternator back in you will blow the diodes out and then you will be facing a very expensive repair bill for nothing. Same goes for the battery, never start the vehicle and then try to connect the battery cable you will again blow the diodes out.