Battery won't fully charge

Question

The battery is about a year old, it held a full charge for about 3 weeks, the voltage sits at about 12.3, that is fine to start the car, but every day I don't drive it, it drops 1 point, so during Thanksgiving it dies over the weekend, then every weekend after that, I jump startedit every Monday for about a month, until that didn't work, AAA came out and started it, I took it back to the mechanic who put in the battery, he said there was a drain somewhere, he kept it two days and said he couldn't find a drain anywhere, and the battery was fine, the voltage was 12.4, and holding steady, for about three weeks, now it is dropping every night again. I have put it on a trickle charger and a fast charger twice, all day long, the voltage won't go above 12.4 The charging system and alternater are fine,while it is running the voltage stays between 13.7 and 14. 7. March I took a 9 hour road trip, when I got to Vegas, the voltage was still 12.4, when I got back it was the same, but the next morning it read 12.6, it started to drop 2 days later though

Answer 1

I'd also suspect something draining on the battery, but alternatively the batter could be discharging internally. I don't expect the latter though. It's rather easy to find a drain if you're a bit lucky, so here's what you can do to find the drain:

1. Shut off your vehicle. Disconnect the positive terminal on the battery, and place a multimeter (in high current mode) between the battery pole and its terminal. Your alarm may go off, try to disable it.
2. Locate all the fuseboxes your car has. Mostly the main boxes are under the bonnet/hood, or in the side of the dashboard where the door covers it when closed. They can also be in the side of the boot/trunk, under the dashboard at either the passenger or driver's side and sometimes in a box under the floor at the feet end or under the seats. Sometimes they're hidden behind a storage compartment lid, they can be hard to find so google for it.
3. Find the legend that contains the information about what each fuse powers. Usually it's in the inside of the lid that covers the fusebox, or there's piece of carton or a sticker nearby explaining the fuses. Sometimes it's written in the driver's manual delivered with your car.
4. Try to find out what the main fuses are, they're usually bigger or different from the rest. A main fuse may power multiple sub fuses next to it.
5. If it's been 15 minutes since you disconnected the battery, note the current that the multimeter is displaying. The 15 minutes are meant to be sure any draining devices have been put off or on stand-by by now. A leak current of less than 0.1A or 100mA is normal. Most vehicles have a little leaking current. If it's more, it's a serious leak, go to the next step.
6. Now it's time to go hunting. Take out the first main fuse. I'd start with the one powering audio/navigation related stuff. Or else the alarm. They're usually the drainers. Note if the current goes down. If not, move on to the next (main)fuse and repeat. If there's a drop in current, that's where your drain is. If it's a main fuse, find the sub fuses it's powering and take them out one by one, noting the current drop each time. You can isolate the drain to one device.
7. Once you've isolated the draining device, you know what to replace. Sometimes it's a big control unit, they can be expensive. If it's audio or navigation related stuff, and you don't want to invest, you can just leave out the fuse and not use its service anymore.

Happy hunting.