Have your price checked the latest DECT 6.0-based phones at your local Best Buy, Target, Walmart or MicroCenter (if you are near one) - there are some good ones on Overstock.com - base/main unit with DAM plus add'l sets - under $80 for all, depending on features? Replacement batteries, when available, are always expensive and they do eventually wear out just like our NiMH batteries used for assorted remotes.

Practically 99% of them come with the keypads & digital circuits for VM, plus other optional/enhanced features - including Bluetooth interface to mobile devices. We don't use the set's VM either and just turned it off.

With new battery replacement in the handset, they are supposed to reset automatically and re-establish programming default, but, you might want to lookup the user's manual on the proper sequence to do a master reset ... Panasonic & others are excellent in that they maintain online support & links long after the models were discontinued - saved me the trouble of digging for the manual on DIY. Perhaps your non-working ones will come back to life with a reset ...