which batterys shuold i exspect to weaken 1st, the transmitter batt or the truck batt? how do i know when the truck batt are getting weak thanks

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.

the batteries in the vehicle will go dead first, since they are moving the servo's, applying brakes etc, you can tell when the steering starts to get sluggish off the ground, if you get a failsafe it will turn the brakes on when the batteries get too low and you cant drive it.

gotta get a high quality fail safe though. Many of the cheaper fail safes tend to shut down prematurely and at many inopportune times.

does the radio range rely more on the batteries in the transmitter or receiver?

tranmitter, thats what sends out the signal