Switching out batteries

Is it easy to switch out an additional battery to the existing battery wiring on the TM? I'm learning all this.... and going to invest in another battery so I can run two. I'm not at all "electrical" savy.... that was my husband... an electrician... so I'm electrically challenged. You'll have to spell it out for me, please. Don't have my TM yet... getting it hopefully this week... at least start the process.