I am using a BB Javelin (8900) and the USB cord isn't recharging the phone. Any ideas?

Does your Desktop Manager recognize your device? If not you may have a faulty USB port.

I am almost certain that this is not the problem, here's why:
a. The same USB cord recharges the phone just fine on my work PC.
b. My BB Curve recharges fine on the same Mac that the Javelin isn't.
c. I tried different USB ports on my Mac but non work.
d. The Mac doesn't really have a Desktop Manager per se (I use PocketMac for syncing), but as I have mentioned my Curve has no problem with this Mac.

Could be the phone, the battery or the charger. Start with the least expensive item to replace first: the charger. If a different charger doesn't resolve the issue, try a different battery.

Alos, cleaning the contacts on both the phone and the battery might help.