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I originally posted this on another forum, but decided to duplicate it here due to the value it offers to CBG and amp / preamp builders.


For some here this may be old-hat.  But for new builders or those who have zero electronics experience (like me) this info can come in handy.

AA, AAA, C, D or 9v?
    The question most people have is Which battery for my project?  We have AAA, AA, C, D, 9v as our main batteries.  But there are also 12v batteries available for higher-power needs.  So I thought it might be good to pass on what I've learned about these power sources.

   So, do you want to use a 9v battery, or six AA?  What is the difference?
   The voltage is the same either way.  If you have a 9v amplifier you're going to need to supply it with 9 volts.  It doesn't matter how you supply the 9 volts (so long as it's DC).  What matters is the amp hours (Ah) the batteries provide... because that will determine how long your amp runs before the battery supply is dead.
   Different batteries have different amp hours (Ah).  Batteries are rated in Volts and Ah or mAh (milli-amp hours).  1000 mAh (1 Ah) means it can provide 1 amp of power (at the listed voltage) for 1 hour.  6Ah means it can provide 1A of power for 6 hours, 2A  for 3 hours, 3A for 2 hours or 6A for 1 hour (it's directly relational).  The Voltage rating is of course whatever that battery offers, 1.5v and 9v being the most common.
   So a 9v battery with a 565 mAh rating (.565 Ah) will provide 9 volts for a little over 1/2 hour at a 1A power draw, or 1 hour at a .5A power draw.
   This list states how long a battery will last at 1amp power draw (depending on the brand).  I'm going to be using Alkaline battery ratings here because they last the longest:

AAA   860 to 1200 mAh (averages about an hour)
AA    1700 to 3000 mAh (90 minutes to 3 hours)
C     8000 mAh (depending on brand, 8+ hours)
D     10000 to 25000 mAh (yes that's 10+ hours on a 1.5v 1 amp device!)
9v    565 mAh (about half an hour)

   So as we can see there are significant differences in battery life. When buying batteries it's good to go to the brand website and check the specs on their batteries.  Those specs will reveal the listed mAh of the specific battery... and all the hyped commercials will become a moot point.

AN INTERESTING CORRELATION
   Consider a portable amplifier that requires 9 volts @ 1A draw.  What's the best battery choice?
Six AA batteries will provide you with 9 volts for about 3 hours.  But what if you hooked up 9v batteries in parallel.  How many would you need for the same thing?
   Since 9v batteries provide 6 times the voltage of a AA, but only have about 1/6th the lifespan of a AA... you would need six 9v batteries to do the same thing as six AA batteries.  Since AA batteries are considerably cheaper than 9v batteries... AA would be the best choice.
   Given the same situation, six C batteries will provide 8 hours of power. Fortunately most 9v portable amps don't draw all that much power (some as little as 200mA or .2A), so you should be able to get several hours of use out of a 9v battery for a small amp.  But if the device requires more voltage or amperage (larger speakers), the larger C batteries may do better.  It stands to figure that a 2A device is going to require more battery power than a .5A (1/2 amp) device... four times more to be exact.
   The Roland Micro Cube is an amazingly power-conservative amp, providing approximately 20 hours of power on six AA batteries.  If you've ever heard the MicroCube, you know it's one of the more powerful of the personal portable amps.  It's no lightweight when it comes to putting out sound and volume.  

12 VOLT BATTERIES
   There are a number of 12v amplifiers available, ranging from Ebay to Amazon to old radios out of a junk yard.  But how do we power a 12v amp?  Aside from lugging around a very heavy car battery, there are a couple of good options.
   Eight D-cells or C-cells.  Eight standard batteries in series provides the power and life to run a 12v amp.  They are however a bit pricey, especially rechargables.
   Scooter battery. A scooter battery looks somewhat like a sealed car battery but is much smaller and lighter.  It is common for such a battery to offer 12 volts at 7 to 10 Ah.  So if you have a 2A automobile amplifier, an 8Ah scooter battery will power it for 4 hours.  Good thing is:  they're rechargeable using a standard auto battery charger.  You can get scooter batteries on Ebay or Amazon for about $15 and up.
   Lithium Rechargeable.  A new line of small, rechargeable 12v battery packs are hitting the market.  Lithium based, these are small and light-weight and carry anywhere from 3Ah up to 10 Ah.  These are about the size of a large deck of cards and weigh well under a pound.  At around $25 these provide a lot of power and small size and weight at a reasonable price.

AMPS IS AMPS
   Within reason, total amps isn't a problem when powering devices.  For example, what if you have a 1A device and your battery is rated at 7Ah; are you going to fry your device?  Nope.  The device will draw only as many amps as it needs.  So if your device is 1amp, a 7Ah battery will last for 7 hours.     The "extra" amps won't fry your board (within reason.  I wouldn't recommend hooking a 65 amp car battery to a HoneyTone amp).  Same holds true for wall warts; so long as the voltage and polarity are heeded, you won't hurt your device by using a wall wart that offers "too many amps".   However, you will need to use at least the minimal amperage the device calls for.  For example if you have a 2 amp device and try to use a .5A (500 mAh) wall wart, your device will regularly cut out due to too little power.

RECHARGEABLE OR REGULAR?
   Rechargeables are great because they can be used over and over.  However in general they have considerably less amp-hours, less life per charge than alkaline batteries.
   For example, as stated above an alkaline C battery contains about 8,000 mAh of use (8 hours at 1 amp).  Comparatively a rechargeable NiMH battery offers only 6,000 mAh... 25% less.  Sometimes that difference can be as great as 50% (depending on battery brand and quality).  So if you need long life go with Alkaline... at greater expense because they will die and need to be discarded. If you don't need that long a life but wish to save money over time, rechargeable batteries may be your choice.     New Lithium rechargeables last longer than NiMH and are getting to the point they're almost the same price.

WHAT ABOUT WATCH BATTERIES?
   You can find those small, flat, 3v lithium-powered (non-rechargable) batteries on Ebay or your nearest dollar store for a song.  Would they be good for powering amplifiers?  To find out go to Wikipedia or the battery company website and check out the ratings on the battery in question.  This is good personal research to find out whether three 3v watch batteries would do as well as a 9v.

THAT'S ALL I KNOW
   That's about the full extent of what I know about batteries.  Hope this helps you in your battery needs. If you have any questions feel free to post them.  Perhaps I or someone else will be able to help if you have special power requirements.

-- Wayfinder

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* The answer:  a typical CR2032 watch battery can contain anywhere from 200 mAh to 565 mAh depending on the maker (cheap HongKong knockoffs vs Panasonic). So the power available differs widely... as does the cost.  The HongKong batteries sell for about $5 per dozen.  Panasonic cost $5 each.

So if you were going for 9 volts, you would need 3 Panasonic watch batteries (in one wired pack) to equal one standard 9v battery, or nine of the cheap knockoffs, wired parallel in 3 packs.

WF, Great summary!

I have a lot of experience with Lithium-Polymer batteries as I fly RC Electric planes...  Most amps I have played with are rated 9-12V and could run on a "3 cell" pack (11.1V nominal), 2200 Mah packs start at $15-$20.  

There are serious downsides to Li-Po batteries, though:

1.  Do not discharge them below 3V/Cell.  So a 3 cell pack (reads about 12.4V fully charged)  should never be charged below 9V, or you will damage the battery.

2. Charging requires a Lithium specific charger.  Failure to use a compatible charger will result in a Serious explosion!

  - Overcharging LiPo batteries causes them to generate gasses, causing the package to swell, and ultimately burst.  Contact with Oxygen then results in immediate fire...

But, yes, I run a 9-12V cheap amp on a 11.1V lipo battery and it works great!  However, I am resigned to the fact that if I forget to turn it off, the battery will be a throw away...

RE: Scooter Batteries:  These are classified as Lead-Acid batteries, and are also used in alarm systems for standby power, and small Uninterruptable Power Supplies (UPS) for computer equipment.  These IMHO, are your best bet, as the typical model has good energy density (AH rating) and are durable.  You can discharge them low, and bring them back with a relatively cheap automotive battery charger, like you said...  Most of what you will see here are using a gel electrolyte, so spills are leakage are not generally a concern.

Good points.   I totally forgot to explain where to find amp-ready 12v batteries.  Here's a few links:

AMAZON

ASIN: B00MF70BPU is a 12v rechargable battery that offers 6Ah.  It will run a standard 2 amp amplifier for 3 hours.  About $30.  Charges with a standard USB cord.

ASIN: B00935L44E  double the price at $60, but 10Ah and offers 5v, 9v and 12v options.  THE battery. :D   Charges with a wall-wart, included along with just about every adapter known to man.  Pricey, but hubba hubba.  5 hours of playing time, totally rechargable, works with just about any battery-powered amp.

ASIN: B0009GIKNE  Amazon's best-selling 12v battery, this is a standard lead-acid rechargable "scooter" battery.  It boasts 8Ah and at $17 and free shipping... the price can't be beat.  Just build a clip-on wire lead that ends in a standard power jack you steal from a wall wart, and you're good to go.  I have two of these and they work great.  Harbor Freight (and just about any hardware store) sells a "trickle float" battery charger for about six dollars that works great in charging these.  Or you can charge them with any standard auto battery charger.  If one is looking for inexpensive rechargable 12v power, this is the way to go.

Great info, thanks for posting!

Follow-up:   Need to convert a 12v battery to 9v?  Here's a terrific device at an amazing price:

DC 4.0~40 to 1.3-37V LED Voltmeter Buck Step-down Power Converter M... 

Ebay item #: 311218237071

At under 3 bucks, it can't be beat for what it does.

Good stuff Finder,as always,you've done the yards,and given detail,kudo's

Always glad to be of help!   : )

Hi,

I want to add a little about the LIPO batteries.

I too mess with radio control devices and use LIPO batteries for all my guitar related power needs.  I will admit that choosing batteries for the application is not so simple.  The radio control supply companies have a "lot" of lithium battery choices.

LIPO batteries are packaged by the number of "cells" per pack.  Each cell has a nominal voltage of 3.4 volts and an actual voltage rating of 4.2 volts when fully charged. [I have never seen an explanation for this discrepancy.]  So, a two cell pack will produce 8.4 volts, a three pack will produce 12.6 volts, and so on.

The LIPO battery packs are manufactured in a large variety of power or amp-hour ratings for each voltage.  When we size a battery for an electric motor, we use the motor's power specification to figure out what size battery in volts and  amp-hours will do the job.

For guitar petals I have been using two cell, 2200 mili-amp-hour LIPO batteries and they run about 2x longer than a regular 9 volt battery.  My current petal battery is a Turnigy nano-tech 2200mAh LIPO battery nominally rated at 7.4v but actually producing 8.4v when fully charged.  Even though the pedals specify 9v input, 8v works fine.

The problem with LIPO batteries is they must be charged with a LIPO battery charger which can cost from under $20 to $100.  A lot of these operate from 12v DC power source and are meant to be connected to an automobile battery.  I use a computer power supply to power my LIPO charger when I am home.  The really good part is they can be recharged 1000 or more times.

Theoretically LIPO batteries are not supposed to be discharged below the 3 volt level.  And, I am careful about this.  But, several years ago I lost a motor glider in December and it was found in February.  That battery spend almost 3 winter months completely dead.  That's been 4 years ago and I'm still using it to power an amp.

I also use a $4 buck transformer to reduce the LIPO 2-cell, 8.4volt, voltage to the 5.7 volts that my Roland Cube 10-GX requires.  This Cube must have an input voltage very close to the 5.7v specification.  By the way the Roland Cube 10-Gx is and excellent little amp.  It's my favorite amp at home and for busking like demos.  It's very light, not expensive and can be run from a LIPO battery with a buck transformer or the provided wall wart.

Fred


John Sawyer said:

WF, Great summary!

I have a lot of experience with Lithium-Polymer batteries as I fly RC Electric planes...  Most amps I have played with are rated 9-12V and could run on a "3 cell" pack (11.1V nominal), 2200 Mah packs start at $15-$20.  

There are serious downsides to Li-Po batteries, though:

1.  Do not discharge them below 3V/Cell.  So a 3 cell pack (reads about 12.4V fully charged)  should never be charged below 9V, or you will damage the battery.

2. Charging requires a Lithium specific charger.  Failure to use a compatible charger will result in a Serious explosion!

  - Overcharging LiPo batteries causes them to generate gasses, causing the package to swell, and ultimately burst.  Contact with Oxygen then results in immediate fire...

But, yes, I run a 9-12V cheap amp on a 11.1V lipo battery and it works great!  However, I am resigned to the fact that if I forget to turn it off, the battery will be a throw away...

RE: Scooter Batteries:  These are classified as Lead-Acid batteries, and are also used in alarm systems for standby power, and small Uninterruptable Power Supplies (UPS) for computer equipment.  These IMHO, are your best bet, as the typical model has good energy density (AH rating) and are durable.  You can discharge them low, and bring them back with a relatively cheap automotive battery charger, like you said...  Most of what you will see here are using a gel electrolyte, so spills are leakage are not generally a concern.

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