I have recently bought myself a Giant Fathom E+ 3 and it is a beautiful eBike. Originally I was going to buy the Fathom E+ 2 with the Energypak 500 battery but I decided on the Fathom E+ 3 with the Energypak 400 battery instead. However, I would like to buy the Energypak 500 battery for my Fathom E+ 3 for the added capacity and range. How easy is it to replace the Energypak battery on the Giant Fathom E+ eBikes? Please advise.