Getting one but tough decision. Putting it on an xpress h51 17x50 with a 50 merc.presently have a mg 45 pound thrust. 12 volt. Will a terrova 55 12 volt work or do I need to go to the 80? Problem is fitting another battery under the rear deck. Money is not the problem. Space is. Never had a problem with with the 45 but never pulled cranks cranks either. Help will be appreciated.