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I've come up with a plan to make a potable mobile charger for my galaxy phone with a rechargeable 9 volts battery.My original mobile charger(220 VAC input) says it gives an output of 5VDC at 0.7 amperes and hence I decided to make it with the given ratings.So here's my plan-I'll use a 7805 to regulate the 9VDC from the battery to 5VDC.The 7805 gives a maximum of 1 A output.So here's my question should I use a current regulator(LM317) to limit the current from exceeding 0.7 amps or will the phone's battery draw the sufficient amps from the LM7805?Maybe it might be a good idea to assist the output with a resistor as a safety measure.So,what do you say?

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You don't need to limit the current. The phone's charging circuits will only pull the amperage it needs. It can probably handle more than 700mA anyway and charge the phone faster. You'll also want a couple of capacitors to help you smooth out the voltage from the regulator. This instructable may help a bit.

https://www.instructables.com/id/Universal-USB-Power-Supply-Kit/

What kind of 9V battery will you be using? Don't use a standard 9V rechargeable battery cause they don't last very long and probably won't be able to fully charge your phone from a single charged battery. You would be better off with 6 AA or AAA rechargeable batteries. They will last much longer that a single 9V. Better yet would be getting a long lasting lithium battery and charger to go in your setup.

Okay,so change of plans.I came across some rechargeable AA batteries(1.2 volt,1900mAh).What if I use 4 such batteries so that they would give out 4.8 volts(which is close enough to 5 volts) ?and I wouldn't have to bother about the amps since they give out much more than what my phone's battery really need and like you said "it'll draw only what it needs"

You won't GET 1A from a 9V battery. Using a 7805 will waste 4W as heat constantly while charging.

If you want a battery charger, look at "mintyboost"

The phone WILL only draw what it needs from the charger, so you shouldn't limit it - it will draw one amp.

so right you are Steve,I completely forgot about the battery's mAh and thanks for the tip on wastage of 4W as heat.I searched for"mintyboost" and got interesting results.But please do tell me what exactly does a "mintyboost" do?

Look it up