Cannot open Sentry Safe ESB-3 batteries dead, cannot find keys

To order replacement keys, for small chests and files, you will need to know the key numbers which can be found right around where the key goes in. It should be a stamped number, letters, or both located around the keyhole. For Personal, Home and Home/Office Safes, you will need the model number and serial number. I think that the most economical place to buy keys is from www.SentrySafeShop.com. You can do a search for "lost keys" and it will give you a screen where you can enter your model number and key number. (It is a very easy screen to use. They just need 1.)Model # and 2.)Serial or Key #.)

In Summary:
For Small Chests or Files: A lock reference number is required. It will be a letter, a number, a letter and number, or "blank" (no letter or number), engraved/located on the silver cylinder of the lock. These are model numbers 0500, 1100, 1170, etc...

For Personal, Home and Home/Office Safes: (model numbers will begin with: S0, S3, S4, S5; I0, I3, I4, I5; A3, A4, A5; J3, J4, J5; L0, L3, ,CS,CSW,DA,DS,KS,KSW,MS,MSW,OA,OS,and SC): Indicate your model number and the safe serial number found on the front right-hand side of the door, between the hinges.
Here is the direct link to the key replacement screen: http://www.sentrysafeshop.com/Keys-Sentry-Safe-Replacement-Keys-p/keys.htm