Sears continually changes their website navigation.

From their home page, key in a search for "DieHard Portable Power 750".

Alternatively, link to their "Automotive Section" ==> "Batteries and Chargers" ==> "Battery Chargers & Boosters".

You're looking for the battery, and not the inverter with the same name

Mastervolt sells gel cell batteries for marine applications. Needless to say, the operating environment on a boat can be quite harsh. This site is for the more technically inclined as you'll need to piece together a solution from this company.

At one point they sold smart chargers with world-wide compatiblity.

This recommendation comes from one of our U.K. customers (thanks, Bill)

• Battery - Search on: "12V Sealed Lead-Acid Battery
  
  
• Charger - Search on: "12V Sealed Lead-Acid Battery Charger"

Maplin is a very popular site amongst British electronics hobbiests.

Another popular site amongst British electronics hobbiests (thanks, Bill)