Mike - it is a sealed AGM battery.

Here's the scoop:

680 cranking amps for 5 seconds
595 cranking amps for 10 seconds
525 cranking amps for 20 seconds
Short circuit current over 1800A
17Ah
25 minute reserve capacity with 25amp load
CCA - 220
Female brass terminal w/M6 SS bolt


Here's the sales pitch
Better warranty - Limited 3- and 4-year full replacement warranty - not pro rata.
Longer service life - With 3-10 years of service life, ODYSSEY batteries save consumers time, money, and aggravation.
Longer cycle life - 70% longer cycle life compared to conventional deep cycle batteries - up to 400 cycles at 80% depth of discharge - high stable voltage for longer periods of time.
Longer shelf life - Can be stored on open circuit (nothing connected to the terminals) without the need for recharging up to 2 years or down to 12.00V, whichever occurs first.
Faster recharge - The highest recharge efficiency of any sealed lead battery on the market - capable of 100% recharge in 4 - 6 hours.
Mounting flexibility - Non-spillable design - can be mounted on any side in any position except inverted.
Vibration resistance - Design protects against high impact shock and mechanical vibration - a common cause of premature battery failure.
Extreme temperature tolerant - Operating temperatures from -40oC (-40oF) to 80oC (176oF).
Totally maintenance free - No need to add water, ever! Drycell design with resealable venting system.
Improved safety - US Department of Transportation classified as a 'non-spillable' battery. No acid spills, no escaping gases.

Model: Odyssey PC680
PPS SKU: 37L105S5
Shipping Weight: 14.25 lbs
Availability: Stock / 24 Hours
Manufactured by: Enersys
Dimensions: 7.15"L x 3.00"W x 6.61"H
Voltage: 12 Volts
Capacity: 16 Amp Hour(s)
Chemistry: Lead
Terminals: M6 Female Brass
Case Material: ABS Plastic
Case Color: Black/Orange Top
Internal Resistance: 7 milli-Ohm
Battery Type: VRLA/AGM
Internal Composition: Lead/Tin
Plate Material: 10 Hour

Mine will be installed on its side -
If you do go with this battery, make sure its at a PC680T or MT as the normal purchased configuration is just an 'L' terminal for motorcycles though if you are using bolt on terminals, you can save a few bucks by ordering just the PC680.

Another that Roger Spears suggested is the XS Power 680 size. Virtually the same specs and size. I just happened to come on a 'super price' one day, which seems to be gone now