The #1 reason a generator fails to start is battery failure. Maintenance and inspection are critical. Make sure your charger has power and is working properly, sometimes the battery breaker becomes tripped shutting it off or is turned off for maintenance and not turned back on. Make sure there are no loose connections, clean the battery posts and connections as necessary. Batteries should be replaced with new ones every 3 years. I would recommend having an outside generator company do a semi-annual inspection and annual preventative maintenance. If the same company takes care of your generator set from day one they will have the full history to work from. If you take these steps your batteries will perform when you need them most, in an emergency.