Heart rate monitor weirdness

I ran between work and my massage appointment tonight. My heart rate monitor gave me some very strange numbers, both high and low. Do they start giving erratic results when they need new batteries? I'm just assuming the watch part of it is fine, since electronic stuff either works, or it doesn't work, and there is very little in between. Maybe it's time to move to a Garmin. I don't really mind a $70 timex lasting a year or so and pooping out, but I'd be choked if a $400 Garmin only lasted that long.

The IGP said aerobic, so I ran 4 x 9/1 trying to maintain a pace where I was breathing deeply and evenly, but not gasping or panting. That was supposed to work out to a heart rate in the low 130's or so, but it was all over the place so I stopped looking at it. My legs were feeling good, so I started with some light stretching, about 5 minutes walking, then running at what felt like a strong and confident pace. Things felt very natural and smooth, until the last few minutes of the run. Then I got tired and sloppy.

I wasn't really trying for a fast time, or any time in particular, I just wanted to run for 40 minutes at a strong pace. It just so happens I looked at my watch at the 5 K mark, and it said 32:15, but the heart rate was also 168 or something impossible like that.

People have asked how I'm doing with the one arm pushups. I actually tried one during the long stretching after the run, in our new workout area. My total is almost exactly one half. My physio therapist pummeled and contorted me this morning. My massage therapist worked on some of the same stuff in my arm, but also found lots of other owies. I ought to sleep really well tonight.