According to my husband, you can never have too many batteries.
The greenie in me would like to add: Or rechargable units.
And right now you can get a sweet deal from Amazon.
Get the Duracell Mini Charger, with Two Pre Charged, AA batteries for only $4.69 (regularly $17.23) when you click on the $3 off coupon and checkout thru Subscribe & Save.
Remember: All Subscribe & Save orders ship for free and you can cancel your subscription anytime after your order ships. Read my Subscribe & Save tutorial if you need more information.
Amazon pricing can change on a dime, so always confirm prices before you check-out.