“Will I need to maintain a minimum balance?”
You're starting a bank account. Some bank accounts charge a fee if you don't keep enough money in the account. You ask whether this bank does that.
Will I need to maintain a minimum balance?
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(someone) will need to (do something)
This expression is for talking about things that will be necessary in the future:
You'll need to check in with the host when you get there.
I'll need to come out and take a look at it before I can give an estimate.
maintain a minimum balance
Some bank accounts require that you keep a certain amount of money in the account. If you have less money than that, you'll be charged a fee. The amount that you have to keep is called the "minimum balance", and keeping more money than that number is called "maintaining" a minimum balance.