Charging NiMh in series?

I have 6 D cells in series in my radio and I put a wire from a jack to the battery contacts in the radio. So they are connected in parallel with the radio, while it is running.

I have been charging the batteries by plugging in a wire from a 9.45 voltage adapter from my 12 volt batteries. Maybe it would be safer with an 8.4 volt adapter?? But would that destroy the adapter???
I need to know if these can be over heated by leaving it plugged in too long. At 3 hours they are not hot or even warm but I am afraid to walk away from them for long.
I was charging them with a so called smart charger, but it took all day.

Ps; I know how everyone wants answers to questions on this forum, but I can't get back to the internet until to marrow.

9.45volts is fine that`s 1.57volts per cell , 8.4 volts would not charge them completely at 1.4volts , what capacity are the D cells mah and how many ma is the charger?

John.

Another thing to consider is that charging batteries in series will likely lead to shorter battery life. When batteries are charged in series, it is inevitable that one battery will be fully charged before all the others are. This means that fully charging the pack will inevitably overcharge that battery (and any others that charge early). For this reason, charging batteries in a smart charger with independent channels is best. But if you must charge them in series, keep the charging current at low as possible. This will increase charging time. However, overcharging is MUCH less harmful to a battery when the charging current is low (which is why 'dumb chargers' always charge with very low current).

the batteries are 1000 mAh and the adapter, not a charger, is 1 amp.

so maybe I should try using the lower voltage adapter if it is safer.

1000 mAh or 10,000 mAh?

Charging 10,000 mAh batteries in series at a maximum of 1 A would be fine as it would amount to a 0.1C slow charge.