Is it possible to use a lead-acid battery as a power bank?

Question

I have an Oxygen 6v 4.5Ah lead-acid battery. Can i use it somehow as a power bank to recharge my cellphone? Your response and help will be greatly appreciated.

Answer 1

You should use a low dropout voltage (LDO) regulator, which is a type of linear voltage regulator, to reduce your battery voltage (which could vary from about 5.6V when empty to about 7.2V when charging) to the 5V required by your phone.

There are many to choose from; LT1529 is a good choice since it comes in a TO-220 package, is stable with a single 22 uF output capacitor, and has a version with a fixed 5V output rather than needing two resistors to set the output voltage. You can buy one, and the necessary output capacitor, on Digikey.

You may need to do something with the USB data pins (connect a 200 ohm resistor between them, short them together, tie them to ground or +5V, or make an intermediate voltage with a potential divider) to make the cellphone charge at full rate. Google should tell you what it needs to be for your particular cellphone; the first method I mentioned is the official USB standard but not all cellphones support it yet.

Answer 2

Yes. All batteries store energy, just like flywheels, compressed springs, inflated balloons, and food. Power, being the time integral of energy, is what you get when you convert the stored energy in any of these things to some other form of energy.

Your battery has a nominal voltage of 6V. All you need is a device that will convert that to a voltage compatible with your phone, and is compatible with the physical specification of your phone's charging port. USB is popular and requires 5V, plus some additional signaling to indicate that the USB port is capable of more current (for charging) than typical (for running a keyboard). 6V is close enough to 5V you might not need to convert the voltage, or it might force the smoke out of your phone. It's probably out of specification, so it's hard to say without trying it, which I wouldn't recommend.

Or if you want to take a roundabout, inefficient path, you can connect an inverter to the battery, converting the battery's terminals to a physical specification compatible with that normally available from a wall outlet. Then connect your phone's factory charger to that.

Answer 3

6v is so close to 5V that a linear regulator will usually be about as good or better than a fancy switcher. A simple lm323 regulator is rated for 3A max the 323 does in fact need more than 6v and won't work, but there's an LDO variant that I forgot the part code of that does.

You might have to short the data pins of connect a resistor to them or something. Chargers do something odd with the data lines to tell the phone what they are.

Or, get another identical battery, put them in series for 12v, and use a normal car charger type thing.