It should be fine to leave them on the charger, but the bigger concern is temperature. I'm not familiar with Elk Grove, but if you get below-freezing temps, you will want to bring the batteries inside for the winter. Freezing temps are bad for batteries. They can get damaged.
Gary, the length of time you can leave on the charger depends upon several factors. Does the charger have a monitoring device built in? What does the manufacture say about doing this? Type of batteries this device uses. Leaving them on the charger for a day or so should do little to mess things up. However some newer batteries have memories and if they are charged incorrectly will not charge as deeply the next time you run them down and recharge them. And then again some can be left on charge all the time.
Follow the manufactures advice on this. If you do not have any info I would suggest you Google them and find their 800 number for service. I am sure they can provide the correct information that your looking for.