http://safemanuals.com/ let me know if i helped rate me please.
Your batteries are either no good, or not charged. When you press the PTT button it takes more energy than being in standby mode. If you have a battery problem it will fail quickly when the PTT is pressed.
Rechargeable batteries last approx. 18-24 months. Check your battery for a 3-digit date code. It is usually a 3 digit number followed by a couple of letters. The numbers tell the date of manufacture. The first number is the year, followed by the week of the year. 025 would be 2010 the 25th week. (or if very old it could be 2000 the 25th week.)
If you feel age is not a problem, you might check your charger(s) to see they are fully powered, and clear of debris on the contacts (and the radio contacts as well). Clean with a pencil eraser if needed.
A few tips: Be certain when placing your radios on the charge they are turned off. Check your wall outlet to be certain it doesn't get shut off with a light switch. Expect to replace your batteries every 2-3 years.
Here is a link to the user guide: http://www.giantintl.com/RadioPDFs/Outdated%20Manuals/T6400_User_Manual_E.pdf
VOX is the word used for voice activation.
Here is an explanation of GMRS: http://en.wikipedia.org/wiki/General_Mobile_Radio_Service
The kebt-650 appears to be a replacement batter for the Motorola Solutions MU and MT Talkabout walkie talkie series.
Contact Motorola Solutions Get Support
Motorola Mobility Support
This is more for "mshtexas" than the OP but I'm sure there may be others out there wondering the same thing. The power cord that comes with this unit has a 9.0v output at 200mA with the center pin being positive