HEADS-UP! If you go beyond 6 MONTHs you are asking for a rude awakening when the safe does not open, and you need it to right then and there (i.e., when there is an IMMEDIATE need to access). Suggest you invest in a decent voltmeter or multimeter and check the battery (ies) BEFORE you install. A 9v battery should be well above 9.0v when installed, mine test at about 9.58-9.64. NEVER use rechargeable lithium, only known-good-quality alkaline.

Also, most strongly consider a dual/redundant-lock – a dial/manual and an electronic. If you already have a safe with only electronics or only mechanical/dial, consider this one that I used on my older safe (the newer one has separate dial and keypad) – https://securamsys.com/products/safelogic-xtreme-emp-proof – or $176 less here (https://mbausa.com/safelogic-xtreme-swing-bolt-lock-package-w-chrome-keypad-rh-mounting/?gad_source=1&gclid=CjwKCAjw3NyxBhBmEiwAyofDYYr5fkOXzlp1X3nJ-FZa_5bEmGiWtRaAMBPvDY3DxzsNUaxNG3-AVhoCjX0QAvD_BwE)