What is the right battery to go with a 140 amp alternator?

what do you mean when you think the battery isn't holding up?

Any 12 volt car battery will work, but I would recommend getting a decent quality one with at least 650 to 700 cold cranking amps. But those cold cranking amps are more critical in cold places, so if you live in a state with mild winters it wont be as important. A decent 12 volt car battery now a days can run from 50 to 70 dollars or more for the fancy ones. Here is a site with some info for you that can help with understanding alternators/batteries. https://www.onallcylinders.com/2015/03/27/alt-text-5-things-you-should-know-before-using-a-high-output-alternator/ Unless you are running a high powered car stereo system, a 140 amp alternator should be more than enough. Good luck hope this helps.