Ok... so here's the deal with my 96 blazer.

The battery is brand new, but it's dying every couple days and constantly needs to be jump started if I let it sit overnight.

Once the battery has been jump started, it will run for as long as I need it to, so that's why I'm thinking it's not the alternator. Even after I turn it off for like 5 minutes, the car will start without hesitation. If I don't run it for the rest of the day and let it sit overnight... it will be dead and will need a jump.

I haven't checked exactly what the alternator's charging at, but I'd assume it's strong enough to keep the car running without dying. I'm not leaving any lights on inside and the keys out of the ignition.

Any ideas?

 

Either your battery is defective,your alternator isn't putting out the voltage it needs to, or you have a bad drain on the battery.
First you need to get a volt meter & see what your alternator is putting out. Second have the battery tested where you bought it. If you have run it dead several times it could have an internal short. Then third try disconnecting thew battery over night & see if it starts OK.

 

Assuming the alternator isn't the issue... how do i find a possible short that's draining the battery?

 

get a multi meter set it on amps, undo the + battery cable, put one end on the battery + post and the other on the + battery cable and have someone start pulling fuses until the meter reads .145amps or less and than go from there.

 

I'll have to go pick up a multimeter. I'm guessing I can probably get one at an auto parts store or a radio shack.

But when you say .145 amps... is that what it should be reading if there wasn't a drain? If I pull a fuse and the amps go above that number... does that mean I found my problem?

My electrical knowledge is pretty novice, so I just wanted to make sure before I start doing stuff.

 

Think of amps as wather flowing through a pipe, each fuse is a valve sending water to an exit, if an exit is leaking the removal of the fuse shuts the valve to that exit.

An amp meter must be put in series with one of the battery connections. Disconnect one battery terminal, connect the amp meter one lead to the battery terminal one to the disconnected cable. Now all electricity that flows through the system must go through the meter first. The higher the reading on the meter the more drain on the battery, each drain poin you disconnect by pulling the fuse or disconnecting should lower the reading on the meter. Your goal is .145 amps or less. as you turn things on the amps will read higher. I suspect a glove box light is on all the time, or the rear license plate light is on all the time. Disconnect/unplug drains one at a time till the amps go down, the one that makes it go higher is the problem.

 

Thanks for that simplified explanation. What you're saying makes sense.

Now... what should a normal multimeter read if there was no drain? You're saying it would read .145 amps or less, right? If that meter is reading something higher, there definitely is a drain somewhere?

So, I basically just need to pull fuses until that number drops below .145?

 

correct. anything over .3amps is a no no and you got a problem you want to be as close to .145amps as possible.

 

I have experienced similar issues with my blazer.

David - I think I am following what you are saying but I too have a very elementary knowledge of electricity and I just needed some clarification: So the flow of electricity should be greatest with all fuses in place then when you pull the fuses one at a time, the one (or possibly multiple ones) that is supposedly draining the battery will cause the greatest drop in amperage as that circuit is disconnected?

i.e. I found that the vanity mirror lights on the back of the visors where not turning off even with the ignition off. So supposing this was the culprit causing the drain, as I monitored the fuses being pulled I would see, just for example, a constant .2 amps and then a significant drop to say .15 amps as the fuse for the vanity lights was pulled?

fyi I just broke the little light bulbs which seemed to be the cheapest solution to the problem.

 

Thanks... I'll go to home depot later and pick up a multimeter and report back.