rule of thumb is to always charge your batts before each run or day...

depending on your batteries in your radio and truck... its hard to tell which will last longer. For example, i have 2400 mAh batteries in my radio and 1400 mAh battery pack in my truggy. My pack in my truggy dies out first.

If your radio starts to show yellow, its time to get ready to replace/recharge the batteries. When you notice a slow response time with your steering and notice weaker braking power, its time to recharge your receiver pack ASAP.