I've repaired a lot them over the years. Yes you can replace the battery yourself if you can find the battery, they are getting harder to get. But it also depends on which model you have. The LED-2 the battery is easy to replace, the LED-3 is a little harder and the LED-5 & 7 timers don't have a battery. If you try to replace the battery and solder it in wrong you'll ruin the timer. If the timer says "Fail" and you reprogram it and it goes back to "Fail" when power is removed then you need to replace th battery. I've replaced all of my older Dixmor timers with the LED-7 timer, they are more user friendly for the car wash customers.