problem with NiMH batteries in digital cordless telephone

I have a problem that is only marginally diyaudio, if one dares consider telephony a form of audio...

I have had a Samsung DECT cordless phone for about 3 years. DECT stands for Digital European Cordless Telephone and , being a small version of the GMS digtal mobile phone standard, has been the standard here for ages. I believe it is known in the U.S. as "900 MHz digital cordless phone", but I may be wrong about the frequency.

Anyway, the NiMH rechargeble batteries were beginging to age. Samsung having kindly chosen the "micro cell" or AAA form factor rather than something proprietary, I chose the highest capacity of AAA NiMH batteries, which happened to be Panasonic 7=0 mAh NIMH "for DECT" batteries.

Just prior to replacement, the old batteries gave me about two days of standby or two hours of talking, which is about half of the original performance. With the new batteries, I have about 6 hours of standby away from the base station and 45 minutes of talking before there are dropouts. Dropouts will occur even with the battery charge meter being 3/3 whereas with the old batteries it had to have been down to 1/3 for a long while before dropout occured.

Is this a problem related to battery selection? Or might something like a cap have given up inside the phone coincidentially?



P.S. The original batteries had green plastic coating with no brand name except the Samsung part number. I believe rated capacity was 550 mAh but can't find the manual right now. I am VERY sure they were NiMH rather than NiCd, both according to package text and manual.