Best practice using second database within module in 3.2.1

Hi, I’m developing a new module M3, which has to access data from a second database. All my models depend on this database m3, which is already added to config.php. Is there a best practise to switch the database within the module , e.g. in mod.m3.php?

I added a service in addon.setup.php

'services' =>array( 
                'm3db' => function ($addon) {
                    return new Database('m3');
                }
            )

Is this a solution? But how do my models know where to be retrieved?

Thanks for help.