Guessing what the voltage is will be hard, so you might consider getting a voltage checker or a charger that shows the voltage readout.
The charger on our website shows the voltage readout. You can find it here: https://swiftpaws.com/products/upgraded-charger-for-home-or-home-plus
If you are using SwiftPaws every day - or every 2 or 3 days, it is fine to charge to full after each use and you'll be ready for the next run!
But if you don't use it that often - it is not recommended to leave the battery sitting unused either fully charged or discharged. You can estimate the voltage based on how long you have used it. Always start with a fully charged battery.
If you only use it for one, two, or three 90 second runs - it should be fine to wait until just before using it again to charge to full.
If you run for the full ten minutes (about five 90 second runs) you might want to put it on the charger for 15-30 minutes and then stop charging for now and when you're ready to use it put it back on the charger and finish charging to full a day or two before you'll use it
For long term storage (over three months) the battery needs to be stored at 11.4v and taken out to be charged and discharged back to that voltage before continuing to store. In this case you should have a way to check the voltage.
The battery voltage should not be allowed to drop below 9.6v
CAUTION: The battery should always be allowed to come to room-temperature before charging. Charging a hot or cold battery might delay charging or damage the battery. For best results, charge the battery at temperatures between 50º and 80ºF (10º-30ºC).
DISCLAIMER
The advice given above is general in nature and you are responsible for the safety of your batteries. SwiftPaws is not responsible for any direct, indirect, special, or consequential damages and personal injuries, including that to life, and health, resulting from the customer’s application and use of batteries sold by SwiftPaws.com.