To add a little more detail...
The slot is at the opposite end of the remote from the key ring attachment. I've outlined mine in red:
A medium slot screwdriver will do the job nicely:
And the battery is (for 2005, at least) a CR 2016 (Radio Shack is indeed likely to have them):
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2008 Starcraft ST 2700BH behind 2005 Toyota Sequoia Limited 4x4.
Linked by ProPride 3P 1400, stopped by Prodigy, guided by Garmin nüvi 760.
2006 Fleetwood Sun Valley - sold March 2009 / 2006 Dodge Caravan - traded April 2008