Bought an '08 TSX about a year ago for my daughter. Car is stock except the previous owner installed an AutoStart remote start.
Been running just fine, except that the fob door unlock doesn't usually work, and opening with the key will often set off the alarm. I blame the above on the AutoStart or the installation, which I need to look into rsn...

The car has been starting and running fine until the last few days or so where it will usually need a jump in the morning to get started. No typical signs that the alternator is faulty, and the battery "born" date is from last year (2018). Granted, I don't know the history of this battery before we bought the car (could have been deep discharged, etc.), but it made it through a cold winter here so I suspect something else before I go pulling the battery or alt. So I measured the current being drawn from the battery using an ammeter and found some pretty surprising (to me) numbers.

At the positive post, seeing about 840 mA after things settle down. Verified this does not ever reduce (watched it for 30 minutes).
By observing the current as I pulled various fuses, I determined the following:

100 mA is going to IG1 MAIN (ignition?) via 50A fuse #23 in engine compartment.
400 mA is going to interior lights circuit via fuse #6 under dash (peaks at well over 1 A at first, as various vent motors (etc.) click and hum.)
340 mA is going to backup circuit via fuse #7 under dash

I don't know the AH rating of a 51R battery, but drawing nearly an amp at all times seems like a formula for a dead battery. I thought I read somewhere that around 50 mA is more typical for a modern vehicle. Ordered a 2008 Acura service manual which is on the way. But I'm curious if anyone here believes these current draw numbers are typical.

 

You have a drain. Off standby current should be < 50 mA. HandsFree is a common culprit. It could be multiple drains. Start unplugging items on affected circuits to find source of drain.

good luck

 

$100 says it's the handfree link under the passenger side right kick panel (beneath the glove box, door side). Big black box with a bright green label on it. One large cord loom plugs into it.