This is an Optima OP34M Blue Top Battery.
Weight: 43.5 lb
C20 Capacity: 55 Ah
Post Type: Dual SAE & 5/16" Stainless Stud
CCA: 750 Amp
CA: 870 Amp
Width: 6 7/8"
Height: 7 13/16"
As taken from Optima's website:
The BLUETOP is a high-performance AGM battery with exceptional running time and more recharges than you’d get out of a traditional battery. On top of providing outstanding vibration resistance, the BLUETOP’s efficient power delivery and faster recharge time mean you’ll spend less time worrying about your battery. This means more time for fun. Again and again. This flexible boat battery and RV battery is ideal for those who need a sure-starting, strong-cranking, maintenance-free power source.