If i buy the normal battle pass now

Probably not. The first 25 levels will likely require less XP to grind. They have probably considered the possibility that people might try to get more bang for their buck by cashing in 25 levels when the levelling curve gets steeper.

Though maybe you will be granted a fixed XP amount equal to the requirements of grinding from 1-25.

Yep. If the first 25 levels are easier to grind its not worth it for me. 

i have the battle pass 950. I don`t see options to upgrade to premium.

Can`t the just add that option to still pay the remaining coins for the premium battle pass.....

Just noticed something in the battle pass tab now that it's been released. You can buy battle pass levels individually after already buying the pass. 150 coins from level 1 to 2. I haven't played yet so I don't know if that's a fixed rate.

true but it will cost a lot more coins.

Yes you can, this was on the QA from EA about the battle pass and the bundle.

What happens if I buy my Battle Pass late in the season?

You’ll receive all the rewards up to your Battle Pass level (which is your current level for the season) retroactively! For example, if you’re on level 20 for the season when you buy the Battle Pass, you’ll unlock all rewards for every level up to 20, plus three special Battle Pass skins.

If you buy the Battle Pass Bundle, you’ll get the rewards for 25 levels in addition to the levels you’ve already reached. So, if you’re on level 20 for the season when you buy the Battle Pass Bundle, you’ll get all the rewards through level 45 and the three special Battle Pass skins.    

That kind of applies only if you don't have any battlepass. If you have a normal one, you probably can't get the bundle anymore (I don't see one, just the individual level buy for 150).

Lvl100 isn't too hard anyway. Got lvl3 today. Although I did play for 4 hours.

If you find out how to upgrade from basic to premium please let me know. I clicked the basic one accidentally and cant upgrade.....no option to buy upgraded pass ☹️

Same here  I'm trying to upgrade and cant  ☹️