According to manufacturers if the battery have a built-in cell balancing system you don't need to change it. This would for most newer batteries.
Allegedly, If you try to charge a battery that doesn't have the balancing system you will be putting excessive power to some cells that would charge faster and this will damage them.
Because the bike's alternator charging rate is usually around the 800mA mark to 12V and it will drop above this figure up to 13.8V. This will allow a slow charge that won't affect much the individual cells.
Keep in mind that Li-on batteries are made of several cells of 1.2V connected in serie to add up to 12V and in parallel to make up the operating current.
However, as I said, newer batteries have the CBS built-in.
This is only for the bike's charging system and not for a external charger.