Andronikos,
When I replaced the battery on my K1600, I went with a EarthX 680, a LIFePo4 battery, and an Optimate battery tender. It's much, much, much lighter than the original lead acid gel cell, and with the Optimate tender, should outlast me.
I don't remember all of the research I did, but I seem to remember choosing the EarthX because of it's internal cell balancing devices / wiring ... essentially, it means that the battery is fully compatible with standard ICE charging systems, nothing else needs to be added.
If you do decide to go down the same path (LIFePo4 battery and tender), be aware the LIFePo4 batteries DO require a tender suitable for LIFePo4 batteries. When I bought mine, I seem to remember that Optimate may have been the only manufacturer supplying suitable tenders.
Hope that helps,
Dominic