didn't get more than 300+ mA.

But you did get more than the rated 4.5V . Besides, did the illumination on your panels exactly match the illumination in the factory setup when the spec was drawn up?

 

Did the illumination on your panels exactly match the illumination in the factory setup, when the spec was drawn up?

I'm sorry, I don't understand your question.

 

You said "They are rated for 4.5Vdc @ 1.5 watt @ 0.334 Amps output." But the output is dependent on panel illumination. The rating was determined in the laboratory/factory where the panel was designed/made, using controlled illumination of a panel. We don't know what that illumination was, but unless you can duplicate it you can't expect the same output.

 

Also, the output current at 5.0V will be much lower that it will be at 4.5V. That is why you would use an SMPS to convert the panel voltage at 4.5V to a higher voltage if you need the higher voltage to charge the batteries. If you are willing to learn your self instead of asking us to explain every little thing, Google and read about MPPT.