Ok, I received my $15 digital multimeter today (the craftsman that I linked to above). The battery was showing a resting charge of 12.48:
Per the Trojan Users Guide, this appears to be about 80% charged:
I then plugged it into my cheap charger:
It measured 14.8 but slowly increased up beyond 15 (every 4-5 seconds it increased by 1/100th; yes, I stood there for a while!):
I don't really know what that means.
Per the users guide, I seem to be looking for a charge of 14.8 (at least?):