Hello Good People,

Please, I am conducting an independent research on the operations and use of ATMs from the consumer angle and I am seeking informed answers to the following questions:
1. How much is the required minimum balance that should be left in a user's account?
2. How much is the least withdraw-able denomination/amount?
3. How long does it take to resolve a user's ATM related complaint?
4. What is the most common ATM complaint/dispute?
5. Which bank(s) offer the best/worst ATM experience?

To all responders, Please, I will appreciate responses that are detailed with clear references to the specific bank(s) that you are commenting on. 
I am also requesting the same info from relevant quarters in the banks themselves but like I said, this is from a consumer perspective, which is why I am trying to get your valuable inputs too.
Thank you very much.

@feel,from my experience

Minimum balance-1000naira(Skye bank), 500naira(first bank); all on savings account.
Least withdraw able sum- 500naira
How long to resolve issues- 48hrs(Skye bank)
Most common dispute- Account gets debited and customer doesn't get paid
Best and worst experience - Best: Skye, I only need to call the Skye help centre and my issues are resolved,no need to fill any forms or visit my branch.
Worst: Its a tie between intercontinental and UBA, those guys don't know what they are doing

Thanks a million EzzyIzzy.Really appreaciate.
Dudes!! Babes!! Please I am waiting to hear from you guys.
Thanks.