Most manuacturers recommend half a C to 1C charging rate, and a charging time of less than 3 hours, for their lithium batteries.
That mean the charging mA must be limited according to the capacity(mAh) of the batteries.

1C of a 1000mAh is 1000mA and it will take 1 hour + ~2% of an hour to charge it at that rate.
0.5C of 1000mAh is 500mA and it will take 2 hours + ~2% of 2 hours to charge.

If you charge your 2500mAh batteries at a rate of 300mA, or even 500mA, it will take longer than the recommended charging time and may affect the batteries life.

Select the appropriate mA, according to your batteries capacity, to keep the charging time below 3 hours.
If you can't do that with your charger, upgrade to a better one.