Hi RuefulR,
Welcome aboard!
If the charger LED
on the 2000mA charger (which is the one that I included with the SB3) never goes RED, this *most likely* means that the battery voltage is too low for it to be charged. The charger will not go into charge mode if the battery voltage is below approx 10V. What you have is most likely a dead battery, and it needs to be replaced.
Please contact me at vinnie@redwineaudio.com and I will discuss your options to either have me replace it for you, or recommend you a replacement battery (available online) if you wish to try and replace it yourself.
And I was so looking forward to listening to this thing!
That is the one thing that tricky about buying used RWA products... you don't know how the previous owner took care of the battery.

Even if you deep cycle the battery (play longer than the recommended play time) one once with the SB3 (and even if you are still able to charge it), you will significantly reduce its lifespan

.
SLA batteries do not like to be deep cycled, and I mention this in the modded SB3 User's Guide and other info about careful charging habbits. If you did not receive this, I can email you a copy.
If you have any other questions, please let me know.
Best regards,
Vinnie