More current would allow you to charge your batteries faster. To double the current output you need to connect the solar panels in parallel. Connect the positive terminal of one panel to the positive terminal of the other panel and also connect the negative of one to the negative of the other. This will give you a max rating of 3V at 300ma. The circuit diagram below shows the solar cells connected in parallel. You can see that the voltage is the same at 3V but now the current will be doubled.