We have a couple of cordless phone systems in the house, a Uniden and
a Panasonic (they all seem very similar).

In all of them, the handset batteries simply do not last. The
replacements last even less.

I would like to know why this is so: are the batteries poorly made, or
are the charging stations overcharging them? What is the story?

Say, the batteries in my Nikon camera last forever and always recharge
very well on the standard Nikon charger. Similarly, the batteries on
my DeWALT drill also last a long time and are not ruined by
recharging. Further, I have seen many cheap cordless drills thrown out
because of ruined batteries.

Lastly, is there a phone system that is made honestly (like my Nikon
camera), with good batteries and smart chargers? I do not mind paying
a significant premium for that.

To me they all seem to be the same, a lot of cheap software "features"
with bad usability, and bad basic qualities like phone durability or
battery lifetime.

Thanks

i