I used to set reminders on my calendar but would always get tired of snoozing a dozen reminders until I had time to do anything.
I sat down last last year and made a spreadsheet with weekly, monthly, yearly, etc lines and different maintenance items to check. From recharging or replacing batteries to buying extra flashlights. That way I can check off that I did my "maintenance" when the time is best for me and have a log through out the year.