How to use dumb charger to charge rechargeable batteries

Charging my Ikea rechargeable batteries with RM7 Mr D.I.Y. dumb charger

This is how I charge my rechargeable batteries using a cheap dumb charger. Basically these chargers have very low charging current (100mA) and they charge really slow. Dumb chargers does not know when the batteries are full, so the charger will keep on charging even though the batteries are fully charged. By using a 24 hour timer, I set the charge to charge intervals of 1 hour with 15 mins of rest to let the batteries cool down in between. How long should the full charging period be, depends on the capacity of the rechargeable batteries.
For example; using a 100mA charger (check the specs of your charger for this) to charge 900mAH batteries, you will need 9 hours (900mAH/100mA) to fully charge the batteries.

Some people would recommend to charge longer to make sure not to under charge. So the rule of thumb is to use 1.2 as the multiplier. For this case would be 1.2(900mAH/100mA) ~= 11 hours.

My personal preference is to use the 9 hours charge. Even though I am under charging them, at least I don't spoil the batteries by accidentally over charging them.