99 Tahoe not starting?

MMk I've been out and about, in and out all day with the Tahoe and no problems. I go to the rec center, go inside for about 20 minutes, come out, and the Tahoe doesn't want to start. It acts like it wants to-I mean it really was trying to start, but just never kicked in. It's kinda like rarararararara, and then nothing. I noticed there was zero water in that little box that keeps coolant....I had a sealer put in about 6 months ago to keep it from losing coolant. So I put some water in there thinking maybe just maybe that would help. I go to start it again and it does the rarararararara sound and I get nothing. Then I try again and it just does a "click" like the battery is dead. I look at the battery gauge and it's very low. The battery was replaced last year...I believe. So I have someone give me a jump. We sat there for 20 minutes trying to juice it up. The gauge went up a little...just above the red line. There are two red lines. Before that it was in the border line red line. So it got a little bit of juice, but not much. Finally gave up and pushed it in the parking lot, now waiting to figure out what I should do next. Does anybody have any ideas what sounds like may be the problem??