if anyone has the same question about this, hope the answer will help you.
I got the answer from my batteries store customer service team, they are very professional and patient.
several factors can affect the charging time:
1: the capacitiy of the battery, larger batteries will take longer more than charge smaller ones
2: the type of battery, different types of batteries have different charging characteristcs, for example, lead-acid batteries typically take longer to charge than li-ion batteries.
3: the charging method: different charging methods, such as using a standard wall charger or fast charger, can affect the charging time. charging a battery at a higher rate will typically result a shorter charge time.
4: The initail state of a charge: A battery that is completely discharger will take longer charge than one that is partially charged.
5: Temperature: high temperature can slow down the charging process while low temperature will speed it up( but not for all batteries and chargers)
How to calculate the batteries charging time( PS: they also taught me very patiently,haha)
charging time=( battery capacity/average charging current)+loss(1~3)hours.
ex: battery: 1.2V aa 2300 mah
charger( below sepcifications about ebl battery charger, they said it's a slow charger, if fast charger, will charge more quickly)
charger Average charging current (in genearal, the more batteries are charged on a charger the lower the average current each battery can receive)
AA 1/2：500-1250mA @1.2 V,
AA 3/4：250-750mA @1.2V,
AA 5/6/7/8：150-350mA @1.2 V
if I charge 1/2 pcs ''aa 1.2V 2300mAh battery'', and take average data 800mah
Charging Time= 2300/800+loss(1~3h)= 3.5~6.5hours
if charge 8 pcs aa 1.2V 2300mah batteries, take data 150mAh
charging time= 2300/150+loss(1~3h)=16~19hours
For my last question, why my aa batteries takes longer than I expected, because my current charger charges slower than EBLofficial site. they promote battery charger time according to their own battery charger.