You can check for parasitic drain easily. You do this by putting the car to sleep, thenpulling fuses from the engine bay fuse box and BCM fuse box one at a time to identify the circuit that has the excessive drain with a multimeter.
Get yourself a digital multimeter with alligator clips that can measure mA current draw and a small piece of wire also with alligator clips. Make sure the alligator clips are large enough to fit around the battery terminals. Park the car. Open the hood. Open the driver’s door. Get some kind of clamp that can keep the door switch on the door frame pushed in. Now here’s the somewhat tricky part, without fully disconnecting the battery electrical system, connect the wire with alligator clips to the ring terminal on the end of the negative wire and work the ring clamp loose off the battery. Keep the other end of the wire in contact with the battery terminal at all times. Also make sure the wires and terminals never come in contact with any other piece of metal and especially not the positive terminal of the battery. You also do not want to lose the battery connection or you will void the test and you have to start over waiting for the car to sleep again. Now connect the digital multimeter in parallel with the wire between the battery terminal and the wire terminal ring clamp. Turn on the multimeter to the amps or milliamps setting. Remove the wire jumper. Your multimeter will now show a current draw reading from all of the electrical components in the car. Lock the car and take the key somewhere away from the car like opposite side of the house or more than 30 feet away. Wait 5-10 minutes for the car to go to sleep. When you come back, the multimeter should show a very low current draw if everything is working correctly. Something like 20-30mA. If the current draw is higher than that, you have parasitic draw. Now you can take the fuse box covers off (engine bay and driver side dashboard near the door hinge) and one by one remove a fuse, check if the current draw has changed, put the fuse back, and repeat with the next fuse. Eventually you will find a circuit that when the fuse gets pulled the current draw drops to normal.
As long as the alligator clips stay in place, the key is not near the car allowing it to sleep, you don’t disturb the clamp holding the door switch closed while the door is physically open, DO NOT attempt to start the car with the multimeter or wire jumper in place, and you only pull one fuse at a time, then this method will work and tell you what may be causing your issue. If you do this and you can’t find a circuit causing a problem, then you may have an alternator or charging circuit problem and the battery isn’t getting properly recharged. Also, new batteries can go bad. Who knows how long they sat on the shelf or if they just aren’t working right.
