Can anyone point me in the right direction?

I want to set up a charging circuit for a 9 volt battery which will charge once the battery level is 5v and stop when it reaches around 9.

I want to run the charging circuit off an alternator which will only come on when the battery needs charging and once the battery is fully charged the alternator will switch off.

The battery is running a small circuit which can function from 5 - 12v. Hence only charging once it drops to 5v

Is this possible? and does anyone have any examples or circuits.

Thanks

 

What is the 9V battery type.
Nicd or Nimh ?

 

Sorry, Currently I am using a 9V Ni-MH battery, but honestly, if need be that can be changed.

 

You should not take a 9V NiMh battery below 7 volts.

http://batteryuniversity.com/learn/article/discharge_methods

Ni-cads have similar limits, but are much more forgiving about charging precision.

Battery University has more information than all of us could write in a week. Read it!

 

To beat#12's reply you will kill your battery doing that, no matter what the battery is supplying.

Are you intending to build your own charger (not recommended) or adapt something off the shelf?