My computer is a 7 year old IBM Thinkpad R31 series, factory installed battery still in place. I rarely, if ever, use battery power, am always connected to an AC outlet. Battery power usually stays at 98% but today it has dropped to 0%. I am a computer novice so I don't know what this sudden drop means, will I damage my computer by continuing to use it? Should I purchase a new battery? Help will be appreciated. Thank you.