I have quit a few talkabout T7400 we bought a few years ago. None of them are working. I can tell you that they were being put back in the chargers in the on position. Is there a way I can test the...
To answer your questions:
1) The light on the charger should come on and stay on, when a radio or a battery is charging. It is not likely all the chargers would go bad at the same time. With this in mind, check your charge contacts on ther radio and the charger. Clean with a pencil eraser if needed. Try charging a battery outside of the radio (if you have a drop-in base), just to see if you get a constant red light on the charger. If not, your charger or possibly the battery is bad.
2) If you have a voltmeter you can check for existing charge in the battery. It will not tell you charging capacity, but it will tell you if it is flat dead or not. Check the date code on the battery. It is a 4-digit number on the back portion of the label in the white area. It will read as 1121, 11 is the year, 21 the week of the year. NiMH batteries have a 2 year life expectancy. And as you indicated, charging with the radio turned on, will age the batteries quickly. It is not good to leave the batteries on a charger with the radio turned on, or for extended periods of time, such as weeks or months. A few days won't hurt occasionally.
3) Lastly, your radios may need serviced. You could have charge/accessory jacks which are worn out, if you are using the wall plug style charger only, and do not have a drop-in base. If they have been anywhere moist they could have grown corrosion and be non-repairable. However, if they are dry and otherwise free of defect they should be repairable. (Current expected flat rate repair is $69 at a dealer who works on this model.)
Best regards
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