There was a recent article stating that 'modern' gel/ no maintenance batteries can be a problem, compared to old fashioned lead acid batteries. Modern batteries have the advantage that they self discharge a lot more slowly than lead acid batteries. I was thinking offitting one to my 1958Triumph STA but Arthur at Rockerbox advised against it. Lead acid batteries don't start to discharge until they have been initially charged, by filling them with electrolyte. So a lead acid battery can sit on the dealer's shelf for many years without being affected. Modern batteries have a limited shelf life and can self discharge in storage, even to an unrecoverable state.
The modern batteries which have the most capacity and quickest charging cycle are Li po (Lithium Polymer). Used in electric powered model aircraft they all come partially charged although it doesn't say so on the packaging! They also have a horrible capability of bursting into flames during charging and must never be left unattended during charging. Note that Li po is metallic, and once metal starts burning there is nothing which will put it out. This is why Li pos are not used in cars.
If buying a modern battery for your bike get one from a main dealer and check how long it has been in stock, or buy a new lead acid one.
David Stracey, member 3761