how to choose a good battery charge for laptop

Today,more and more laptop battery or laptop battery replacement appear in my life.so i am searching a good universal adapter.but the queation is how to choose.
one day,i enter yahoo answer,some people give me many advices.
First,you must be sure what kind of adapter,ac or dc,yes, i need a ac adapter,and a new universal ac adapter,because i have a lot of laptop battery.
Second,i am based in UK,I must buy a adapter 's input volt is AC 100V-240V .
ok,i finish primary work,next i need find a expert and cheap laptop battery shop to buy it.
if you need also a ac adapter,i hope the story can be helpful for you.