Disable Spotlight indexing, save battery life
Well, the immediate way is:
sudo mdutil -i off /
from the command line (you will have to enter your admin password) to stop indexing immediately.
You might also want to add the following step:
sudo vim /etc/hostconfig
(you might want to use a different editor than vim, YMMV)
Then, navigate to the entry
SPOTLIGHT=-YES-
and change it to
SPOTLIGHT=-NO-
SAVE the changes the exit the file. BTW, have a look at iFixit on how to change the battery, it seems you could have much better use of the laptop that way.