First of all, thank you for your book :)
I am tackling with a 1 meter, arduino controlled boat project whose thrusters are SeaBotix BTD150. Data sheet: http://www.seabotix.com/products/pdf_files/BTD150_Data_Sheet.pdf
I confused about to select suitable batteries. I dont want to use lithium batteries due to risk of fire. I think to use SLA batteries (2x 12V) but they are heavy. Can you help me for finding logical batteries for these motors?