12V BCI Group 65 AGM Powercell Battery. 
Can be used as a reserve and/or starting battery.

Specs:
Voltage : 12V
Wattage: 3000W / 4000W
MAX Amps: 3900
CA: 1100A
Ah: 86
RC: 174min
 
Dimensions:
Weight Lbs.: 53.81 lbs
Weight Kgs.: 24.41 kgs
Length: 11.8 in
Height: 6.8 in
Width: 7.2 in
 
M6 Terminal Hardware Included.