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.