Having an issue with my battery (I think). To preface, I installed a small powered sub in my mini last week but just started having this issue today. Not sure if it’s correlated or not. Here’s the context-

I went out to dinner and after getting back into my car after an hour or so, the battery died. How it happened was a bit odd. I put the key into the accessory on position, and then turned the key after a second of waiting like normal. Right when I tried to start the car I lost all power. Dash went black, no turning over, no lights, nothing. I hooked up my little jumper starter battery pack and it immediately turned on.

I had plans to go to a movie after that, so I went to the theater. 3 hours later after the movie and the car starts right up. I drive home and park to get my mail. My battery dies in the same way it did after dinner. I jump start it again. I pull it into the garage, turn it off, and it’s dead again.

Seems like a parasitic leak? I don’t know why it would be so intermittent though, and if it would die immediately after driving it. Would a bad ground from my amp installation cause that? I have a pretty large gap in knowledge when it comes to electronic issues and can’t find any similar issue online.

Thanks!

 

Intermittent behavior of the type you describe is not a symptom of a parasitic battery drain problem. Rather it is more a symptom of a bad battery.

A battery can be helped to a bad condition by usage but also over time by bad battery connections, cables, ground straps, and an alternator that can fail intermittently. (I had one car -- not a MINI -- in which the alternator started out working just fine but after some minutes of engine run time its output started falling.)

For some model years the car is particularly sensitive to a marginal battery. With a marginal battery the ECU will shed electrical load which stills has the engine starting and the driver thinks the battery is ok but it is not. If allowed to degrade further that's when things can go downhill in one big hurry.

One sign of a battery problem when preparing to start the engine and the battery low symbol lights up, can be an orange battery symbol in the rev counter panel, with a message in the speedo panel stating that the battery needs to be charged, or something similar.

It is critical the replacement battery be the right one in terms of not only fit, and battery post location, battery venting, but the same CCA and AH. And if the battery can be "registered" with the car's electronics this must be done.

 

Did you by chance monkey with your battery cables when you installed the sub (you should have), and if so, have you checked that they are tight?