When should I change the battery?

I have a 2004 Honda Accord with just over 26 thousand miles and the
original battery.

Is it time for me to replace the battery yet?  On the one hand, I do
NOT believe in waiting for the battery to go bad.  Some people say
that can tell by the fact that they need to crank a bit longer to
start the car, but I'm not sure I'd notice.  Even if I knew I would
notice and avoided getting stranded, I'd rather get it done at my
leisure rather than have to drop everything I'm doing to take care of
it.

On the other hand, the fact that a Honda battery (assuming it isn't
the original one, which is warrantied for only 3 years, with the last
year prorated) is warrantied for 100 months (first 3 years fully
warrantied, remaining term prorated) makes me think I could wait at
least another year.  The general rule I've heard is to replace a
battery a year before the warranty expires.

I live in Iowa, so I'm not subject to the battery-killing heat of
Phoenix, Las Vegas, or Tucson.  Of course, I've heard that very cold
temperatures (like last winter) are also bad for car batteries.