Super power packs for cordless telephones

I use the Varta Phone Power on the phone, because the age and with constant charging only slightly.
The last had been 3 years in there and still have 70% of its rated capacity of 800 mAh.
The batteries last charging cycles of up to 1,000 times, until their power diminishes.
Memory effect I can not confirm.
I only charge the phone when it is empty.
So not every phone on the charging station, after.
I am speaking here exclusively of our cordless phone. As the batteries
behave with other devices, I can not say. You are also only for Use
Telephone thought.

From me, there's the full 5 star and a strong buy recommendation.