When should I change the battery?

park at the top of a hill, turn the headlights on for 10 minutes with
the engine off, then see if the starter still cranks healthily
afterwards. if not, look for batteries on sale. if it's completely
dead, roll it down the hill to start it.
if you have a battery charger, you don't need the hill and you save
some wear and tear on the alternator.

 

You can replace the battery every 5-7 years. Johnson Controls sell
store branded batteries and OEM branded batteries. You can get these
for <$50. It's cheaper than a Honda alternator.

 

If you can find an AC Delco maintenance free it's even better than the
JCI, only $30-40 more.

 

Take it to your local Autozone, and they'll test it for you
for free (at least they did for me)...