The speaker is for the Robbe Navy sound module. Now the boat can make different sounds like: destroyer siren, engine sounds, ship bell etc. There is no room for a spare battery. There are three batteries on board. A 6V-3Ah battery for the middle engine, a 12V-5Ah for the two outer engines and the sound module and a reciever battery (The red one in the electrinics module).
I tested the boat today and i am very pleased with the performance but I lost two of the three props

. I forgot to fasten them enough. I learned that the weight distribution wasn´t optimal so i changed the lay/out of the ship (see picture)
Regards John