If you have only one battery and its Diesel, check its cranking and cold cranking amps. Its best to have as close to 1000 CCA as possible. Also a second battery helps. Group 31 batteries are usually beefier as well. if you have or opt for dual batteries replace or install them both at the same time and ALWAYS CONNECT THEM PARALLEL!!!
red to red, to starter black to black to ground. 12 volts.