Subject: internal resistance of battery using voltmeter

I have looked through the archives already, but none of the existing questions 
are specifically related to finding internal resistance with a voltmeter. I 
have worked through the following problem, but I'd like to know whether or not 
my answer is reasonable (or correct). My question involves how to calculate the 
internal resistance of a battery given a set of parameters. For example, if a 
voltmeter whose resistance is 1000 ohms measures the voltage of a worn-out 1.5 
V battery as .9 V, how do you calculate the internal resistance of the battery? 
I've tried to work through this problem a number of ways, but I keep getting an 
answer of about 700 ohms, which seems unreasonably high for the internal 
resistance of a battery.

Re: internal resistance of battery using voltmeter