Originally Posted by lucid
Cleveland, it sounds like you had an alarm system that was drawing significant current. I don't have an alarm system. The only possible load on the system is CA when the ignition is off. So, your comparison is off, and how much current CA will draw is not determined at this point.
The specific battery under consideration does have the required cranking amps.
The specs state that it will last 3100 charging cycles at 10% DOD. It seems like what we need to know is how much of a load CA constitutes exactly, and if that exceeds 10% DOD when the car is parked for a couple of days or not driven enough for a full charge cycle.
Oh Lucid, I only glossed over one or two of the issues that I went through trying to make this work in both cars.
You don't even know the half of it...
When I tell you that I was determined, I'm DEAD serious. I wouldn't give up, because I really thought I could beat the odds that were stacked against me.
I thought this way for about FIVE YEARS
. No one could convince me otherwise.
I had "a plan"...or so I thought...
The E36 Alarm fiasco was just the tip of the iceberg. That was merely one of many road blocks I had to overcome.
Another instance was the Bluetooth/ASSIST module in my E46 M3 that was drawing a load when it was supposed to be in 'sleep mode' when you kill the car. I was surprised to see how even a small amp draw affects these batteries.
It wasn't enough to kill my big OEM battery, but it wiped out my little Odyssey battery in no time. You wouldn't think these batteries would drain so quickly, but I found out the hard way they can and will.
My point is, you and I both know that your margin for error with this particular mod is significantly reduced with a smaller racing battery. (less than half the size) You can't afford to leave anything on in the car for very long, or you will end up stranded somewhere just like I did about four years ago.
I had to flatbed the car because I decided to stop at a mall out of town and forgot to kill the courtesy lights on the car.
I was only inside the mall for about an hour (less actually), but that was enough to drain the small battery past the point of no return. It was late Sunday afternoon (all the auto parts stores were closed) , and I had to call a damn tow truck to flatbed the car back home. That was an expensive and embarrassing situation that could have been avoided. I put myself in that awkward situation. I know it was my own fault, but that just goes to show you how easy it would be to get yourself into a lot of trouble.
Just food for thought, I think the battery size you are trying to use is too small for the electrical demands of the M3, and it will come back to haunt sooner rather than later.
Other members are quick to tell you how "cool" this mod is...well, it's not all peaches and cream. (that's for sure)
But hey, it's your call.
I just thought you might like to know the other side of this story...