A fully charged battery will last for about 10 minutes of motor run-time (or about 5 play sessions). Always use the charger that comes with your SwiftPaws battery - or one that is compatible.
If you purchase a compatible battery elsewhere, make sure you to use the charger that is recommended for that battery.
As your battery ages, you might see a decline in performance. Your battery will need to be replaced once it reaches 80% of it's original capacity.