There has been quite a bit of discussion over recent years about which battery is best to use in the V-Max. General consensus seems to be an AGM (lead-acid absorbed glass matt) type battery offers the best performance available and most reliability for a high performance large displacement application like the V-Max. Don't confuse this type battery with a gel type, it isn't (the AGM is superior). These batteries require no maintenance and have a much longer shelf life before discharging. Two common batteries discussed these days are the 'Odyssey' and 'Genesis' batteries by Hawker, both being basically the same battery marketed under different names. They are both 16 amp hour units and cost about US$120.00. An alternative is discussed below.
BMW motorcycle owners have been using the Panasonic LCX1220P with much success, and it turns out that it's a perfect fit for the V-Max and the very reasonable price makes it even more attractive. The battery is a hefty 20 amp hour unit which more than adequate for even high compression modified motors. The internal resistance is higher than the Odyssey/Genesis so cranking capacity is a bit less (but more than adequate) and overall capacity is greater. It is also a sealed AGM type battery requiring no maintenance and has been used successfully by quite a few V-Max owners and owners of a few other makes of motorcycles with similar battery size needs. Once you try a battery of this type in your Max you'll never go back to the traditional stock lead-acid type.
The Panasonic fits in the stock V-Max battery box with no modifications.
Specifications for the Panasonic can be found here
The best price currently for the Panasonic battery is US$47.95 + shipping from the business below. Purchases may be made online through Portable Power Systems. Shipping will be added to every order (also during checkout). There are no taxes (except CO) or handling charges added.
Order a Panasonic LCX1220P here from www.apexbattery.com - $47.95 + shipping (add $2.05 filler to get free shipping)