I'm not sure if this is the right forum for this question, but here goes. What size (Group) starting battery is suggested for an NS18E2 (Nissan, 18hp) motor?
According to page 9 of your owner's manual at http://www.tohatsu.com/tech_info/own_man_pdfs/Toh9-9D2_15D2_18E2.pdf you want at least 40 amp-hours. In other words, any healthy marine-rated battery will do. Most use a group-24 starting battery, but even a small AGM will work fine. Just don't go with a gel-type, as the unregulated alternator output will probably cook it.
