My first piece of advice, Sebastian, would be to take your time and read up on PV battery charging systems first. There is tons of information out there on the web and in book stores. Where you might read what I have to say and not understand it fully, some one else could explain it to you in a way that "clicks" with you. So, don't rush in to it.
Pictures, wiring schematics and, charts help a lot!
On the back of each of your 3 PV modules, Sebastian, there should be a label stating the output of the module at standard test conditions or STC.
What is the value given for Vmp or maximum power Voltage?
This will discern the nominal voltage of your battery charging system and the type of charge controller you will need to utilize.
For example: If the Vmp on your PV modules is 17.4, then it is consider to have 12 volt nominal charging abilities. Although each PV module can be wired in series with an additional 1, 2 or, 3 more identical PV modules to obtain a higher nominal voltage system of 24 volts, 36 volts or, 48 volts nominal and most charge controllers will work here, !!!provided that all of the other criteria are met!!!
On the other hand if the Vmp is high like, 67, then you will need to wire them in parallel and utilize an MPPT charge controller that can reduce the voltage to a nominal battery voltage as described above ie; 12, 24, 36, or, 48. !!!Again, calculate the other criteria!!!
Because you stated, "So I need to buy one battery and charge regulator for installation." I am guessing that you want a 12 volt nominal system?
To size the wire, fuses and, charge controller you will need to look on that STC label again for the value beside Isc or short circuit amperage and add 156% to it.
For example: If it happens to be 4.56 then simply multiply 4.56 X 1.56 = 7.1136 or, rounded off to 7 amps.
If there is more than one PV module wired in parallel then you will need to multiply that by the number of PV modules.
!!!Also look on that STC label for the maximum fuse rating or maximum series fuse rating!!!
A good place to start. -
www.homepower.com - Once your there, click on, "THE BASICS" and it will lead you to more detailed information.
When I first ventured into PV battery charging I was given a year subscription to this magazine by a colleague. I kept up the subscription for many years and I feel like it was my best investment, by far!
Thousands of dollars, PV modules, batteries, charge controllers, inveters and all have come and gone but the knowledge of how to utilize them correctly and safely has been priceless.
I don't know invented the phrase but it applies here -
"Knowledge is POWER!"