Cannot open door because battery low and i have lost my key. How do I open my safe?

The video shows one way, but the easy way is open it with the back up key, and the battery compartment is in the door. Replace the batteries and reset the combination, but make sure you do it with the door open.

ELECTRONIC DIGITAL SAFE

UserManual.wiki https://usermanual.wiki > ... PDF Slide the Battery Cover off of the Battery Compartment, remove used Batteries, and insert four new "4, AA" Batteries. Once you have changed the Batteries, be ...
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A1 Locksmith Burlingame CA 94010 have Sentry safe locks, keys, battery holders, battery door covers, and door handles. But only a small supply in stock.

e-bar is not a battery problem, it means the door lock is jammed, either use a rubber malet or your balled up fist and after inputting the code to unlock hit the door of the safe all around the key pad as hard a you can, your will hear the rods moving and unlocking the door. Hope this helps. I know it works I do this at the hotel I work in.

Heat the safe, should bring the batteries up enough to open it. worked on mine.

After opening the electronic safe (with the pre-set factory code of 159B) locate the small red button on the
inside of the door near the hinge.
2. Press the red button and then release it, you will hear a beep. DO NOT SHUT THE DOOR UNTIL YOU HAVE CONFIRMED THAT YOUR NEW SECURITY CODE HAS BEEN ENTERED CORRECTLY.
3. With the door open, enter your own personal security code, which can be 3- 8 digits long, and confirm your new code by pressing the letter “B” on the electronic touch pad. Before you close the door, try the new security code to make sure the lock release the knob so you can turn it and retract the live action locking bolts.
If the code fails, go through steps 1-3 again. If the code works successfully, then you should lock the safe. When you open the safe in the future enter the security code you have set followed by the letter “B” and turn the knob.

If the incorrect security code is entered 3 times you will have an automatic lockout for 20 seconds before you can try your code again. If the incorrect security code is entered 3 additional times there will be a 5- minute lockout before the code can be tried again.
BATTERY REPLACEMENT
This safe uses 4- AA batteries. Under normal use, batteries will last about 1 year. When the battery is low, a red light will come on warning you that the battery is low. To test the batteries, enter your security code. If the batteries are low the red light located in the middle of the top of the keypad will start to flash.

To replace the batteries, open the safe door with your security code and turn the knob. Push the batteries cover plate, which is located on the back of the door, and replace the old batteries.
YOU MUST PROGRAME YOUR SECURITY CODE AFTER YOU REPLACE THE BATTERIES. SEE STEPS 1- 3 UNDER “ENTERING YOUR SECURITY CODE”.
TROUBLE KEY
A “Trouble key” has been provided in case you forget or lose your security code. Remove the small central panel from the front of the faceplate. Insert the key and turn it counter clockwise. Then turn the knob on the door towards the right. This will manually open your safe. If you lose your key, you may purchase a replacement key by referencing the serial number located under the central panel by the lock.
MAINTENANCE FOR KEY AND ELECTRONIC SAFE
If the door of the safe starts to rub on the door frame, open the door per the instructions above. By the door hinges you will find a threaded stem. Use an Allen wrench to tighten the threaded stem. This will help realign the door and give you trouble free access to the contents of your safe.

I need an instruction Manual for a Nutool sf20 safe

If the batteries are flat you will need a key to open your safe, the keyhole is usually under a plastic cover on the front of the door.
If the batteries were getting low a light should have warned you.
Hope this helps.

The operating instructions on the ES20 as per the crappy manual:

Open safe using emergency key provided

Insert batteries in the box inside the door

Opening the safe
a. pre-set factory code 159
b. input 159 (the yellow light will flash and the buzzer will beep), then press B or A button, the green light will be on, rotate the knob clockwise, pull outwards, the door is opened

Closing the safe: close the door, input the code (the green light will flash for 5 secs). Turn the knob anti clockwise, the control system will activate and the safe will be locked

Changing the code: open the safe, press the red button located inside the door, the yellow light will go on indicating the code can be changed. Input the new code (1-8 digits), then press A or B button, it shall be confirmed by two beeps indicating the new code has been accepted and stored. If the yellow light and buzzer beeps 3 times the code is invalid - try again

Emergency Key - store in secure place NOT inside the safe. Remove the override cover in the centre of the face of Safe (its a silver plastic panel with Sandleford Electronic Safe ES20 on it), insert override key (a cyclinder key) - hidden underneath the override cover panel - and turn anti clockwise, rotate the knob clockwise to open door

Changing the Battery - If the red and green light are on this indicates that the batteries are low and require changing. To ensure the batteries have been installed correctly test before closing the door

References:
1. Operating instructions EA Electronic Safe
2. http://www.secustar.com/products-en/estype-safe.htm

This manual will answer both of your questions.
http://www.sentrysafe.com/pdfs/OwnersManuals/501664.pdf