Dick_B wrote:
and discovered that they should only be recharged 7 hours per day!
Where exactly did you find that tidbit of (mis)information ?
While it is possible, I guess, it is HIGHLY unlikely.
Note: We have had Panasonic and Vtech cordless phones. Both have NiMh batteries and stay on charge 24/7. I think the batteries in the Panasonic's lasted 5 years. Replacements were not that expensive.
BUT....what the OP reports sounds a LOT like a digital fault and could be with his Voip circuit. Changing the battery or using a different phone for a while would be a good place to start.
Power cycling the VOIP equipment might be a good idea too.