A great website for self education is:
Battery tutorial Alkoffman explained the correct wiring. Each cell of a battery is 2 volts, wiring them in paralell maintains 12 volts, you are just doubling the size of each 2 volt cell-so to speak.
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2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA.
" My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy