Old Buick wouldn’t start. All the warranty on the battery was gone so I replaced it. No problem for a couple days. Now car won’t start. Jump starts and runs fine. A couple days later if I try to start it, won’t start again. Sound like an alternator to anyone? I’ve checked to make sure all interior lights are out, radio is off, and anything else I could think of that might be draining the battery.
OK, if you suspect a draw pulling your battery down, or your alternator is not charging, you need to perform two different diagnoses, both are fairly simple. But in order to do either, the battery has to be recharged to full, generally 12.65 bolts. You need to find out if the place you bought the battery from can charge it for you, then load-test it, to verify the battery is good. If they can't, an auto parts store (like AutoZone, Advance or O'Reilly's) can charge and load-test it, generally for free. Anyway, once you have a battery in the car, hook up *only* the positive cable. Take a 12 volt test light, which can be bought almost anywhere, and hook it between the negative terminal on the battery, and the negative cable connector. If the ignition is off, and all doors and trunk are shut, under hood light bulb removed, and the test light is not lit at all, there is no draw. But if it is and the filament is brighter than dull orange, you have a draw. Keep the test light in place, and disconnect the voltage regulator, looking to see if the light goes out. If not, then disconnect the battery charge cable (be careful not to allow it to touch ground), and same thing. Then, if it's still on, pull each of the fuses in the fusebox. Keep going to try to make the light turn off. If it doesn't when you get to the end, then you need a shop that can do electrical work. Start with that, and we'll see if that tells you where to look further.
I vote alternator because it takes a couple days. Wouldn’t A draw kill it the first night? I don’t have a lot of experience with draws except it’s usually the radio. Time for some fancy blue tooth and touch screens!