I also have the TST 507 system with color monitor. I just had a problem with the monitor going blank and not able to turn on. Long story short- do not leave the color monitor plugged in to power all the time. Just charge it as needed and it will last 5-7 days on a charge. Leaving it plugged in is detrimental to the batteries. Mine is on the way back from TST after being repaired. The manual states, "Do not keep a fully charged display plugged in constantly." but I missed that.