Andy I have several 9 volt ni cad batterys seven cells 1.35 volts per cell gives 9.45 volts
at full charge and a real good voltage to near full discharge. I have seen 6 volt for cameras and cell phones so 9 is doable in almost any chemistry , just not cost effective. the point here is that we should not present blanket solutions to the forum because many of the users that post this type of question are not aware of the implications arising from misaplication of these schemes. remember assume makes an ass out of you and me unfortunatly it is usualy the person askig that suffers. ,and as Eric said on the hv dc topic it is not untill you have had to live with the tragic consequences that you fully realize the gravity of some of these topics. the best advise to give anyone on topics like this is a pointer to a site that deals with the subject professionaly, not an amateur site
coupled to a caution danger explaination. Terry