Nothing about ‘A’ or ‘B’ batteries here!! How does a manufacturer decide which type of battery to use? Let’s I wanna build a remote control for my latest TV. How do I decide if I want to use use two AA batteries or two AAA batteries? Both offer 1.5v each. How 'bout a boom box? What’s the difference between ‘C’ and ‘D’ batteries for this application?
It has to do with current draw.
The more power the thing needs the bigger the batteries (normally). Another consideration is volume and weight. Sometimes they design batteries that are too small and soon die, just because they want to keep them small and light. Laser pointers are a good example. They have tiny button type batteries which cost a fortune and last nothing but try selling a laser pointer that uses three AA batteries.
As justwannano mentioned, it is related to the current draw of your product. The bigger the battery, generally, the more energy stored, so the longer it can power your product. Say you’re designing a boom box. First, you have to decide how long it needs to run before the batteries are dead- 2 hours? 10 hours? 100 hours? Factor in how much current is needed to power the radio, CD player, etc., and then pick the appropriate sized battery to give that running time.
You can actually use C or AA (or even AAA sometimes) batteries in a D-battery boom box, it just won’t last as long before the batteries are dead (of course, you have to get them to stay in there somehow, without falling out).
Similiarly, you could tape two D batteries to the back of your TV remote and get years of battery life
Arjuna34
If that is true what you said, Arjuna, then why don’t we have a one-size fits all battery box for our products the way they have it in the battery rechargers? Or is it that the the battery companies don’t want you to figure out that you can drop bigger-size battery into your CD player, jiggle with the connections, and get it to play for 40 hours? Boy, if Radio Shack were to sell such tweak products and advertise it…
Although it’s generally true that bigger batteries yield longer life, there is a potential loss of efficiency when using ‘wrong’ size batteries. At this level, though, it might not be much; devices that don’t provide a constant drain, or run at very low current (e.g. tv remote) likely won’t show much difference.
Basically, there’s a curve (of lifetime vs. current drain) representing the characteristic of the battery. Battery life is rated in Amp-Hours, which is the result of multiplying a constant current by the amount of time the battery can sustain that current. But it’s not linear, so there is almost always a set current value for that. For example, a battery with a 1 Amp-hour life might achieve that at 100 mA (0.1 A), meaning it will run for 10 hours. If you run it at 1 Amp, you might only get 40 minutes of life. And if you run it at 10 mA you might not get 100 hours of life out of it.
As a practical example, car batteries have a rating (I think) of 12 Amp-Hours or so, but a practical life of a couple of minutes, since they require several hundred Amps for a second or so when starting.
panama jack
Everything I know is wrong, even this statement.
I thought this is clear from the information already posted. Larger capacity batteries are physically larger, which means bigger battery compartment, which means a bigger and heavier CD player. Not many people would buy a CD player with a huge bulge at one end, even if it played for 40 hours.
It is definitely possible to design battery compartments that can handle several types of batteries. But it has to be large enough to accomodate the largest battery. And as long as it’s big enough to hold D cells, there’s no point in putting AAA cells in it - it won’t last long, and it doesn’t make the device any smaller. It reduces weight a little bit, but that’s it. In addition, such a battery compartment would be complex and expensive - it needs some moving parts that hold a smaller battery in place or be retracted to make room for a larger battery. It makes sense to do this for battery chargers because the circuitry for charging different size batteris is the same, and since they are not carried around during operation, they don’t have to withstand bumps and vibrations.
Another consideration is how common the specific battery is… For instance, based on cost, runtime, and current draw, AAA batteries might be best for a remote control, but the manufacturer might make it run on AA anyway, just because consumers usually have more AA batteries lying around than AAA, if they need a replacement.
There are some CD players that come with an optional battery case in which you add a couple of more AA batteries inside this compartment, attach to the original component, and pray to get 40 hours of playtime. It is kind of bulky in itself.
If they can develop that in order to get you to buy more batteries, then I’m certain that they have the ability, though maybe not the profit margin, to make the one-size fits all product I mentioned above.
I routinely use bigger batteries than the design calls for for the simple reason that I am cheap and would rather haul weight and save dollars.
One egregious example is button type batteries. Those things store close to nothing and cost a small fortune. while this is not practical with a wristwatch you can do it with other gadgets. A 1.5 AA or AAA battery that is exhausted for its intended use still has WAY more energy than a brand new button type battery. I have number of devices like thermomethers, desktop clocks, the bicycle speedometer all powered by these batteries which cost me nothing s they are exhausted from their normal use. These “exhausted” batteries cost nothing and will power the gadget far longer than a button type battery.
I also routinely build powerpacks with D size batteries to power things that call for smaller batteries.
To answer the original question…
A battery stores energy. Period. How much energy a battery can store is primarily dependent on two things:
- Chemistry / type
- Volume
To choose what kind of battery to use on a particular design, you must determine the following for the overall system (unit + battery):
- Average “on” time expected (How long should the unit operate w/ a full charge?)
- Average power usage during the “on” time
- Peak power usage
- Size (volume)
- Temperature range
- Rechargeable vs. disposable
- Liquid vs. solid
- Sealed vs. vented
- Disposal considerations (i.e. some batteries are environmentally hazardous)
- Cost
Panamajack was quite correct when he mentioned the “amp-hour” rating of a battery. But I’ve never cared much for the amp-hour rating because the actual potential energy of a battery is still a function of battery voltage (a 1 amp-hour, 2V battery has a lot less energy than a 1 amp-hour, 12V battery). Instead, I like to use watt-hour (or mW-hour). Watt-hour is an absolute unit of energy, independent of battery voltage.
What about battery voltage? For most applications, battery voltage is a secondary concern. If you need a certain voltage, just put the correct number of cells in series. With most modern electronic designs, battery voltage has become less and less of a concern due to the proliferation of high efficiency, low cast DC-to-DC converters.