Hi there -
I'm having intermittent problems starting my new-to-me 05 SR5 and am having trouble figuring it out . . .each time I have problems it's after sitting all night or more than a day.

It started a few weeks ago - I tried to start her and just got clicks. I opened the hood and saw that the neg terminal was full of corrosion so I banged on it a few times to loosen the corrosion up and tightened the connection. It started just fine after that and started/ran all week no problem.

Then the same thing happened so I cleaned and treated both terminals, checked the cables/connections and reconnected. Started up fine and started/ran fine for a few more days.

The third time I got the click-click-click, I had the battery load tested. It came up fine. The next morning I got clicks again so I put a battery charger on it and it fired up fine.

I bought a new battery and replaced the old one.

Next morning after sitting all night - back to just clicking. I threw on the charger and fully charged the new battery.

Next morning it started fine.

Multi tester shows the batt retained the full charge overnight. After starting it once it dropped down to 12.5 (75%?). Alternator charges at 14.7 at idle.

I am starting to look for parasitic drains, but the fuse to the alternator is really stuck in there and I'm afraid to pry it out.

PLus i need to google and figure out how this multi-tester really works . . . the numbers keep jumping around . ..

BTW the car is all stock. Stereo, too.

Thank you !!!

since the cable was full of corrosion, maybe its also bad.

Was it a Panasonic battery?

So are you still having these problems after changing out the battery? Don't be worried about the voltage difference between the alt output and batt output - that is normal.
You can go to ANY batt shop and test a common car battery and it'll most likely be between 11.5 - 12.5v dc without load or charge. Alternators do put out more. They are made that way.
Definitely clean the cables up and keep them free of corrosion, as that will not allow good contact with the battery post. Also make sure they are on tight.

Thanks chaz - i partially unwrapped the cables - they look good

MikesToy: the firs battery is a brand I don't recognize - came with the car and sold at big o tires, second battery is from costco - kirkland brand. (it was the only thing open sunday around here)

AV1: the new battery was drained down after sitting overnight.

My guess would be a bad connection or the voltage regulator is going. Although this is from my experience from a chevy silverado.

Sears are open on Sundays and they have a varies of Die Hard batteries.

Thanks Skyline. MikesToy: by the time I decided to buy a new batt it was too late to get to Sears in time - thus the costco batt. I am heading to sears today, though! I haven't had much luck with costco batteries in the past and want to rule out that this battery is a bad one. . .

I'll look for an amp meter while there. The one I have only measures up to 2000 uA which is 2 milliamps. I read that a normal key-off drain on the batt is less than 50mA . . .

Here is what I would do:

1) fully charge the battery, hook it up in the truck, make sure it starts.
2) let it sit 10 minutes, disconnect it from the truck and test the voltage. (note the time you tested it)
2) reconnect it and let it sit over night.
4) In the morning disconnect it and test the voltage. whats the difference? (note the time)

If we know how long it was connected to the truck and how much voltage drop occurred we can estimate how much current was being drawn overnight, and then take educated guesses as to what it is.

possibilities:

after market remote start? relay packs in remote starters if wired incorrectly can kill a battery in a night or 2 especially if its cold
after market stereo, amp / subs?

Liq: thanks! I tested the voltage (12.74 at 1:30pm pst) and replaced all the connections. I'll test again tomorrow morning and note the time.

Could it be possible that the new battery from Costco wasn't charged fully when I bought and installed it?

I put it on the charger to give it a full charge last night and it showed full this morning when I checked it. Started right up.

No after market anything on the truck to my knowledge. Totally stock.

I had this happen on my Toyota Corolla and it was the starter that was the problem. Not sure if it's the same thing, but might be worth looking into. I don't think my battery would drain overnight though, but wanted to throw that idea out there anyway, just in case!

also, unless u have a deep cycle battery, most times a reg. one goes bad after it been drained down too far.

Well, I went to Kragen and had the alternator, starter and battery tested. They all came up fine. I bought a multimeter while I was there and am waiting for an hour before I test for a drain.

I also am following this guide which has been very helpful!

http://www.aa1car.com/library/battery_runs_down.htm