There is something weird on our cars, I connected the remote turn on of my external amp to the wire that goes to the factory amp as the remote turn on, it turns the amp on long after the car is turned off, and seems to keep it on a lot. I think this is so the bells work when you open the doors, not sure but my amp has a power light and it is on as soon as I open the door of the car, can't see if it is on before I open the door. This means the factory amp is on as well, I have been looking at batteries, for now the
Braille B3121 21lbs/9.5kg
1380 Pulse Cranking Amps
31 Amp/Hr Reserve
6.6” x 5.2” x 6.8"
Right Side Positive

Tire Rack has them, and they include the bracket.
Weighing in at only 21 pounds, the Braille Lightweight Racing Battery is 10-30 pounds lighter than a stock battery. It improves the performance of many vehicles and is suitable for premium luxury vehicles, extreme audio builds and extreme engine builds with high compression and no alternators, supercharger systems, large cams and underdrive pulleys. Custom car and vintage vehicle owners will appreciate the battery's acid-free technology, too.
Specs
Casing: Polymer plastic
Weight: 21 lbs.
Length: 6.6"
Width: 5.2"
Height: 6.8"
Pulse Cranking Amps: 1,380
Cranking Amps: 742
Cold Cranking Amps: 550
Amp Hour Rating: 31
Warranty: 1-year free replacement