Need technical advice on battery and voltage problems

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Hello,

I have an OLD tape recorder that I wanted to make portable, so I cut the plug and wired a 9 volt battery up to it. It may seem pointless, but It is important to me to use this particular "memo-scriber" machine. My problem now is that I can't afford to buy that many nine volt batteries. I am not looking for great sound, the amp is made to run on batteries and works fine, I'm just looking for a longer street life. I have a couple of 12V batteries around, is there an easy way of converting it to 9V and keep rocking out longer? I know Lithium batteries last longer... is there such a thing as a rechargeable industrial 9V battery?

I have an inverter, but it's massive and I would rather not have to go that route.

Obviously I am no electrician, but any help with this would be greatly appreciated.
 
All lead-acid batteries are composed of 2 V cells. You can use five of them to get 10 V.

You can tap into the 12 V units (six cells) or even cut them up.

How close to 9V do you need to get? The 2 V cells will supply about 2.3 V while charging. You can add large diodes in series to drop about 0.6 to 0.75 Volts per diode.
 
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