There are 2 Possible batteries one is a wall keypad unit the other is a panel unit. You may have a keypad without a battery so depending on your model start with the panel and work back to keypad as panel batteries generally last 3-5 years depending on how much your power went out.
if you have a small panel 4x6 then it most likely won't have a battery and is powered from the panel battery.https://youtu.be/vbp4GIOhMcM
if it is a larger panel 8x12 then it will have internal battery.
On the keypad on top with flat screwdriver one tab on either side will open it. https://youtu.be/kGsCob_OCVQ

The panel unit is about 12x24 but can be any size and was generally beige or light brown generally in a closet or downstairs.
the panel unit has a larger battery about the size of a toddlers shoe box and these you want at least 7 amp hour https://youtu.be/ECI84eCynns

There are 2 Possible batteries one is a wall keypad unit the other is a panel unit. You may have a keypad without a battery so depending on your model start with the panel and work back to keypad as panel batteries generally last 3-5 years depending on how much your power went out.
if you have a small panel 4x6 then it most likely won’t have a battery and is powered from the panel battery.https://youtu.be/vbp4GIOhMcM
if it is a larger panel 8x12 then it will have internal battery.
On the keypad on top with flat screwdriver one tab on either side will open it.

https://youtu.be/wR44mTdjhkw