Hi Jabbran,

If you click on the picture of the charger, you'll see a sticker that reads: NiMH/Nicad, three types of Lipo and Lead batteries, so yes, it'll charge about anything you'll need for the hobby and houshold...

One Lipo cell is 3,7V (4,2V fully charged) so 3S would be 11,1V and 4S would be 14,8V.

The motor supplied with the Arowana is a 1880 revolutions per Volt, so 3S would be 11,1 x 1880 = 20.868 rpm unloaded and 4S would be 27.824 rpm unloaded.
The difference in speed when using the same diameter prop is significant.

5S would be more than 34.000 rpm unloaded and make the boat ballistic (and a handfull to drive controlled)

Regards, Jan.