To store LabQuest units over the summer, shut them down and store them disconnected from a charger. To fully shut down a LabQuest, follow these instructions:
LabQuest 2 or LabQuest 3—press and hold the power button until the Shutdown message is displayed (~5 seconds).
Original LabQuest—press and hold the power button (~3 seconds) until the screen turns black.

For LabQuest 2 and LabQuest 3, remove the battery for long-term storage. This is not recommended for the original LabQuest as you risk stripping the screws/damaging the connector when you take out the battery.

Over the summer, the battery will slowly lose its charge, but will be undamaged. When you return in the fall, we recommend that you fully charge all LabQuest units before using them (8-12 hours). When you first turn it on, it may take as long as 3 minutes for LabQuest to reboot if the battery completely lost charge.

Exposing the battery to temperatures over 35°C (95°F) will significantly reduce its lifespan. If your school storage area is especially hot when the air conditioning is off for the summer, you may want to keep it in a location that remains cooler.

More details on the longevity of the battery can be found at:
How long will the LabQuest battery pack last?

RELATED ARTICLES:
Do any of your sensors require special storage?
LabQuest 2 Battery Troubleshooting and FAQs
How should I organize my Vernier equipment?
Do you know of a good case for carrying LabQuests, LabPros, calculators, and sensors?
How should I wrap my sensor cable?
How do I delete the data files that my students save to the LabQuest?