Help with berries please. X&Y?

Question

I have a politoed with quiet nature, I want to have the berry that will heal it's health after it is on half of it's life and i'm not too sure which berry to use as in the descriptions they say "It may be used or held by a Pokémon to heal the user’s HP a little" or "it restores the user’s HP in a pinch, but may also cause confusion" and things like that.
Thanks

Answer 1

A sitrus berry will recover your health once your health is half or below half.

Here is a list of berries in case you don't want the sitrus berry:
http://www.serebii.net/itemdex/list/berry.shtml

Answer 2

There isn't a Berry that restores 50% of your HP but there is a Berry that restores 25%.

Sitrus Berry

A Sitrus Berry restores 25% of the user's max HP.

Sources: Sitrus Berry - Bulbapedia

List of Berries Bulbapedia

Hope I helped :)

Answer 3

Here is a list of berries that restore HP when health drops below 50%. You pick your berry:

Sitrus Berry - Restores 25% of Pokemon's HP when HP drops below 50%.
Figy Berry† - Restores 12.5% of Pokemon's HP when HP drops below 50%.
Wiki Berry† - Restores 12.5% of Pokemon's HP when HP drops below 50%.
Mago Berry† - Restores 12.5% of Pokemon's HP when HP drops below 50%.
Aguav Berry† - Restores 12.5% of Pokemon's HP when HP drops below 50%.
Iapapa Berry† - Restores 12.5% of Pokemon's HP when HP drops below 50%.

I'd recommend Sitrus Berry, since other berries can cause confusion and restore less HP, but it's whatever you choose.

†Causes confusion depending on nature of Pokemon that eats it.
Source