Battery Question: volts vs. mAh

[jcouto]

I know abosolutely nothing about all the various initials and acronyms when it comes to power and electricity. So I have a question, what is the important number to look for when shopping for batteries. I just bought two aftermarket batteries on Ebay for my 300D. At first I was happy because they were both 1500 mAh, more than the 1200 on the canon battery. But then I noticed that the Canon is 7.4 v and the new batteries are only 7.2 v. Is that bad? What does it mean exactly?

I bought the two spares to go with the two I already have so I have backups for the new BG-E1 grip that I ordered and is on it's way to me via UPS. :D Can't wait for that to arrive!

[tim]

I wouldn't worry about the voltage written on the batteries, so long as they're BP-511/A they should work. The mah marking is the capacity of the battery that you should pay more attention to.

[lancea]

Batteries gradually loose their voltage, so there is always tolerance before a device will simply stop working. The 7.4V battery will almost certainly drop to 7.2V and below. So no, there shouldn't be a problem. As another example, 1.2V ni-cad cells are often used in place of 1.5V non-rechargable cells. In that case, the difference can be sufficient to considerably reduce the time before the device will stop working (and some electronic devices won't work at all). In your case, the 0.2V difference is a much smaller percentage. They may run your camera for less time, but then again because they are new and rated for a higher current, you might even get longer use before they need recharging. I'd be more concerned about the recharging process, but again the percentage difference is not much - so you should be right. I don't think you'll do any harm anyway.

By the way, the V stands for volts which is sort-of the amount of force that the battery can produce, and mAh is milliamp hours which is the rate a which you can draw power from the battery. Have a look at AskJeeves or do a Google search for "about electricity" or similar.

[lancea]

Hi Tim - do you have some secret way of knowing when I've started replying to a question? I'm a bit suspicious since you're not too far away :) :) Hope you're enjoying your new lens.

[tim]

By the way, the V stands for volts which is sort-of the amount of force that the battery can produce, and mAh is milliamp hours which is the rate a which you can draw power from the battery. Have a look at AskJeeves or do a Google search for "about electricity" or similar.

That's a good analogy :) Would mah not be more like the total amount of power that can be drawn from a battery than the rate?

A good site is http://www.batteryuniversity.com

[tim]

Hi Tim - do you have some secret way of knowing when I've started replying to a question? I'm a bit suspicious since you're not too far away :) :) Hope you're enjoying your new lens.

Look out your window :p ;) Nah, I just happen to hang around here a lot, too much perhaps.

[lancea]

Look out your window
I knew it! I could hear the noise of your IS! :mrgreen:

[tim]

I knew it! I could hear the noise of your IS! :mrgreen:

Nah that's my motorcycle idling, in case I need to make a quick getaway ;)

[lancea]

Would mah not be more like the total amount of power that can be drawn from a battery than the rate?
It's a combination, but I didn't want to get any more complex. Just to indicate that, for instance, you shouldn't use it to start a car. If it was just the total amount of power then you probably could start a car with it since it would be so quick. The internals of a camera battery just wouldn't take that though.

[robertwgross]

I would not worry about 7.2 versus 7.4 volts. As long as the battery says that it is compatible with Canon BP-511 or BP-511A, then it will work. The mAH rating is sort of like the number of gallons of fuel capacity in the auto fuel tank. The bigger that number is, the more shots you will get before you have to recharge.

If the voltage number were weird, like 8.2 volts or 6.0 volts, then I would be scared.

---Bob Gross---

[BobL]

It's a combination, but I didn't want to get any more complex. Just to indicate that, for instance, you shouldn't use it to start a car. If it was just the total amount of power then you probably could start a car with it since it would be so quick. The internals of a camera battery just wouldn't take that though.

Sorry to be pedantic but "total amount of power" is not the correct term either. What I think you meant to say was "total amount of energy".

[ron chappel]

Yep- Mah is a good way of understanding the total amount of energy

Another important aspect is how fast the battery can let it all go -e.i how many amps or milliamps it can release at once

Old fashioned NiCads and (the closely related) NiMh batteries are excellent at this.It's one of the reasons that they are still used alot in powertools and toys.They are also the best choice for digicams and flash units.

All battery types all have their benifits and drawbacks-you might like to do a google search and learn about them one day

Very briefly these are:

Alkaline- available anywhere.Non rechargable (there are rechargable types but they are hopless in cameras).Highest energy content (i think-it's been awhile since i studdied this).OK current draw rate

Lithium- Unbelievable shelf life.The best in cold conditions.Highest energy per mass.Expensive!.Very good current draw rate
Rechargable lithium -acurate empty/full reporting (info-lithium only?).Good energy density and current draw rate.Expensive but quickly dropping(?)

Nicad- Extremely good current draw rate*.Rechargable.Inexpensive.Self discharge over time
NiMh- Excellent current draw rate.Rechargable.Self Discharge over time

* Nicads used to beat Nimh quite easily but these days the NiMh tends to be better,mostly because Nicads are being ignored.Present NiMh also hold abit more energy .
*You may notice that i didn't even meantion memory effect.Basically it is overblown myth.
While it IS a real phenomenon it's also extremely rare.Most Nicad battery failures are caused not by memory effect,but by deliberatly running them flat too often -a technique used to 'avoid' memory effect ironically.........

[BobL]

RE: Mah
Now to be totally pedantic. . . . . .

a mAh is a milliamp hour
a Mah is a megayear (as in annum) hour

;)

Cheers

[MarkH]

But then I noticed that the Canon is 7.4 v and the new batteries are only 7.2 v. Is that bad? What does it mean exactly?


Is it bad? - No

What does it mean?
In this case 7.2=7.4, they are actually the same. Due to the chemistry of the Lithium Ion batteries (which is what all these BP-511 batteries are) you get 3.6-3.7 volts per cell, the BP-511 batteries are 2 cells so you get 7.2-7.4 volts (depending on how you choose to measure it). It doesn't matter what brand you buy, the voltage will always be the same.

Similarly I have Ni-MH AA cells that state 1.2V and others that state 1.25V, but same chemistry = same voltage so they are just measuring it differently.

Imagine if you measure a building to the top of the roof and I mearure it to the top of the highest protrution (TV Aerial, Chimney or whatever) and my number is different, is the building any different because my measurement is slightly higher?

The thing with battery voltage is that it does vary tremendously with charge and load. For Example:
with no current flowing the voltage might be 7.5 to 8.6 V depending on how charged it is. I just checked 2 of mine and they read 8.3V.
Under a 1 amp charge it might be up to 11 V.
Under a 1 amp load it might be up to 7.6 V depending on how charged it is.
Under a 2 amp load it might be up to 7.4 V depending on how charged it is.
Under a 5 amp load it might be up to 7.2 V depending on how charged it is.
Under a 10 amp load it might be up to 6.8 V depending on how charged it is.
So what voltage do you quote? While in use the battery will be at a lower voltage than when not in use, but how much lower depends on how heavily it is being drained.
BTW: The numbers under load are not accurate, I don't actually know exactly what the voltages would be under different load, but my point is true regardless.

[PacAce]

Is it bad? - No

What does it mean?
In this case 7.2=7.4, they are actually the same. Due to the chemistry of the Lithium Ion batteries (which is what all these BP-511 batteries are) you get 3.6-3.7 volts per cell, the BP-511 batteries are 2 cells so you get 7.2-7.4 volts (depending on how you choose to measure it). It doesn't matter what brand you buy, the voltage will always be the same.

Similarly I have Ni-MH AA cells that state 1.2V and others that state 1.25V, but same chemistry = same voltage so they are just measuring it differently.

Imagine if you measure a building to the top of the roof and I mearure it to the top of the highest protrution (TV Aerial, Chimney or whatever) and my number is different, is the building any different because my measurement is slightly higher?

The thing with battery voltage is that it does vary tremendously with charge and load. For Example:
with no current flowing the voltage might be 7.5 to 8.6 V depending on how charged it is. I just checked 2 of mine and they read 8.3V.
Under a 1 amp charge it might be up to 11 V.
Under a 1 amp load it might be up to 7.6 V depending on how charged it is.
Under a 2 amp load it might be up to 7.4 V depending on how charged it is.
Under a 5 amp load it might be up to 7.2 V depending on how charged it is.
Under a 10 amp load it might be up to 6.8 V depending on how charged it is.
So what voltage do you quote? While in use the battery will be at a lower voltage than when not in use, but how much lower depends on how heavily it is being drained.
BTW: The numbers under load are not accurate, I don't actually know exactly what the voltages would be under different load, but my point is true regardless.
And the reason for the increasing drop in voltage across the battery terminals with increasing load is due to the internal resistance of the battery itself. The more the current there is flowing through the load and, hence, through the battery, the greater the internal voltage drop across the battery which, in turn, subtracts from the battery voltage at the terminals. :)

BTW, the internal resistance of the battery is linear so, given the no load voltage and the voltage with a 1 amp load, you should be able to calcuate the battery voltages for the other current loads in your example, if you really wanted to take the time, that is. But I think you got your point across with your guesstimates, Mark! ;) :)

[DocFrankenstein]

Imagine you have faucet with water dropping from it... :roll: :D

Voltage is the height of the faucet...

mAh is the rate of flow... "liters/hour"... etc...

EDIT: A water dam is a better analogy.

[SkipD]

Amperes ("amps") is the rate of flow.

mAh (milli-amp/hours) or Ah (Amp/hours) is the ultimate capacity of a battery.

[Keiffer]

From what I understand, the higher the Mah the longer the battery will last.

[Sicily1918]

To add to what was said:

The 7.2 volts shouldn't harm your camera in any way.

Voltage is the amount of potential difference. As was said earlier most devices have a decent tolerance as far as what the operating Voltage is -- over/under Voltage is also what will kill your electronics (overvoltage moreso).

Current (Amps) is the flow of energy that actually powers the device (Voltage is what allows more or less Amperes to flow -- the higher the Voltage, the higher the Amps -- resistance being equal).

mAh is the measure of how many Amps can be delievered by the device (or how many it requires) per hour -- in other words, the 511A battery at 1350mAh can [theoretically] deliver 1.35 Amps for an hour (or 1350/2 = 675mA for two hours, etc.) and then it's dead.

Once again, as was said, your batteries are allowing "only" a 7.2Volt difference while delivering an extra 300mAh. If the camera's resistance is 10 Ohms (for the sake of argument -- I've no idea what it is), then:

1500mAh battery:


10/7.2 = 1.388Amps are needed to power the device, you have 1500/1388 = 1.08 hours (1hr 4.8min) of operation
1200mAh battery:

10/7.4 = 1.351Amps are needed to power the device, you have 1200/1351 = .89 hours (53.4min) of operation
Overall, you're still ahead... whew! I haven't done this stuff in almost 10 years -- still got it, tho ;)

[Poco]

Imagine you have faucet with water dropping from it... :roll: :D

Voltage is the height of the faucet...

mAh is the rate of flow... "liters/hour"... etc...

EDIT: A water dam is a better analogy.

Actually, to be totally anal...

mAh is the amount of water behind the dam.
mA is the rate of flow

[DocFrankenstein]

That's not totally anal... that's me being a moron...

You beleive I got an A in that physics course? :lol:

[lostdoggy]

Will the real Rabbit please standup??? BongBongBong!!!

[felix21685]

all hte info i could see here is good

one thing that i learned..is..dont ever....ever charge lithium batteries over 1C
C being their capacity.if you have a 740 mah batter dont charge over 740mAh
if you use the canon charger that came with your camera you be fine of course.
but i saw that one post about charging at 1 amp and thought i might share this :)

[chucksberg]

Ron Chappel......"You may notice that i didn't even meantion memory effect.Basically it is overblown myth.
While it IS a real phenomenon it's also extremely rare.Most Nicad battery failures are caused not by memory effect,but by deliberatly running them flat too often -a technique used to 'avoid' memory effect ironically........."

I thought overcharging was the leading cause of early nicad failure.

I am suprised at how much you guys know about batteries. In most forums you get all kinds of wrong answers. Everyone is spot on here.

[bauerman]

This is one reason why I prefer the Sterlingtek batteries to my Canon branded batteries - the Sterlingtek's are, I beleive 1800 mAh and the Canon's are 1300. Larger "tank"......to work with.

[MarkH]

This is one reason why I prefer the Sterlingtek batteries to my Canon branded batteries - the Sterlingtek's are, I beleive 1800 mAh and the Canon's are 1300. Larger "tank"......to work with.

I like the higher capacity too.

But I also like the fact that buying 4 Sterlingtek batteries from the US costs me less than 2/3 the cost of buying 1 Canon battery here. (It is actually 40% cheaper for 4 x Sterlingtek batteries than 1 x Canon battery). This is allowing for the shipping cost, and paying extra for courier instead of USPS.

[PacAce]

To add to what was said:

The 7.2 volts shouldn't harm your camera in any way.

Voltage is the amount of potential difference. As was said earlier most devices have a decent tolerance as far as what the operating Voltage is -- over/under Voltage is also what will kill your electronics (overvoltage moreso).

Current (Amps) is the flow of energy that actually powers the device (Voltage is what allows more or less Amperes to flow -- the higher the Voltage, the higher the Amps -- resistance being equal).

mAh is the measure of how many Amps can be delievered by the device (or how many it requires) per hour -- in other words, the 511A battery at 1350mAh can [theoretically] deliver 1.35 Amps for an hour (or 1350/2 = 675mA for two hours, etc.) and then it's dead.

Once again, as was said, your batteries are allowing "only" a 7.2Volt difference while delivering an extra 300mAh. If the camera's resistance is 10 Ohms (for the sake of argument -- I've no idea what it is), then:

1500mAh battery:


10/7.2 = 1.388Amps are needed to power the device, you have 1500/1388 = 1.08 hours (1hr 4.8min) of operation
1200mAh battery:

10/7.4 = 1.351Amps are needed to power the device, you have 1200/1351 = .89 hours (53.4min) of operation
Overall, you're still ahead... whew! I haven't done this stuff in almost 10 years -- still got it, tho ;)

From E=IR, I=E/R, not I=R/E. ;)