How many batteries should i use to turn over a n14 cummins?

More is better. Along with an electric or diesel fired coolant heater.

 

It isn't recommended to just add a 4th battery or any number, Should be done all new at the same time

 

If you can afford it check out the maxwell start module.Its expensive but your truck will start in the coldest wheather.

 

if your not starting, you've got a problem.

it only takes 1 battery to fire up an engine. the other batteries just provide more cranking time. your starter motor draws the same amps regardless of 1 or 4 batteries.

my very first local gig was in a 1984 mac dump truck. it only had one battery. and always started me up for 18 months. only problem i had with the charging system, was the alternator belts breaking.

 

I got 4 on my n14 and 4 on my Detroit. Also have 4 on a couple older cats.

 

I always use 4, add 1 if there's room. Having all new is good advise, but.... Starting is your concern, not the condition of all 4 batteries. A volt meter & load tester will tell you if the batteries are good. Every battery has its specs printed on its label, you can match it up fairly well with the other 3. I've never replaced all my batteries because of one bad one, just take care of choosing your replacement choice.