You have to find out if you have a charging coil if so put the changing kit on and follow instructions.
I bought a new 25 Suzuki bog standard charging kit was £106 which consists of a wiring loom and second rectifier 20mins to fit.
I've just bought a Yuasa 7Ah for my combined gps/depth sounder and the figures say that will last about 8hrs. I may be out for 8hrs on a long day but I'm never running for more than half of that so it's plenty. My backup if I was wrong is I have a Powerline 12Ah battery for my Bravo but that's overkill for inflating the SIB once so I could swap batteries over if need be.