Just make sure you have the big 3 done and that all of your terminations are done proper.
Maybe this will help:
Adding batteries helps reinforce and stabilize your voltage around the 12.6v - 13.2v range depending on a few factors. No amount of batteries will help you above that range. Your alternator is what gives you the high 13's - 14's that you want to see.
If your voltage is dropping below 12.5 ish then you need more alt and battery usually. If you hold high 12's when wanging on it then your battery is doing it's job, but your alt is not enough.
Also, make sure you are using a good voltage meter and not a turd.