Batteries in Series/Parallel & Size

I seem to recall from science class that if you run batteries in a series (top to bottom: pos-to-neg-to-pos-to-neg - you increase the amount of volts. Therefore, three (3) 1.5v batteries would produce 4.5v. If you connect the batteries parallel (all pos posts to pos posts & neg ends to neg ends), you do not increase the voltage, but you will produce the current for a longer time period.

I may them backwards, but if this is correct, why do you need AA, AAA, C, D size batteries? Does the size differential mean they last longer? This must be the case. If you buy a radio, Walkman or whatever and the battery configuration requires 9v, why not just configure it for the little 9v “transitor” battery & save space?

Seeking to understand.

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You have it correct as far as the voltage in series, and the current supply in parallel.

What you may not know is that the batteries produce current by bio-chemical means.
You could certainly wire up enough batteries in series to produce the voltage required to start a car, and maybe even wire up enough in parallel to provide the current draw necessary for a momentary starter spin.
(like maybe 10,000 AA’s)

But in the second case, the batteries would be immediately depleted, because the chemical reaction that produced the current, would be used up.

Circuit design usually weighs the power consumption, vs. the battery types available, and they try to give you something that runs for a reasonable amount of time, on the power sources available.
Different circuitry definately requires different battery capacity to meet the current demand, as well as the cost of the batteries.

For an example of bad design, I bought a digital delay pedal for guitar use. It ran on the standard flat nine volt batteries.
It would entirely deplete one in only 1 1/2 hours of use, at a cost of $2.50 per battery.
The current drain was high enough that a rechargable wouldn’t even work. This baby wanted high quality alkalines only.
I can guarantee they sold plenty of $20 ac adaptors for these current suckers.

AAA, AA, C and D batteries are made in different diameters because vibrat // I mean flashlights come in varying sizes and beam intensities.

Size DOES matter. But back to the OP, flash lights take the heavy duty D cells because (in addition to the high current demand of the light bulb) they are devices you may be dependant on for longer periods of time, like during a power outage. Batteries in “emergency” devices tend to be of the beefier variety for this reason.

Manufacturers are going nuts over portability & compactness these days, and because of this you can find a tiny walkman or voice recorder that operates off of a single AA or even AAA cell. If the device has a current-hungry component in it like a motor or a backlit display, it probably takes at least two or four AA cells. D cells might be more appropriate in this case but they just don’t fit into the low profile personal portable devices being made today. You can line up multiple AA cells and still keep a fairly low profile.

You’re more likely to find D cells in things you can toss into your garage or junk drawer.

Hello ConMan,

You’re basically correct that cells in series add their voltage, while cells in parallel divide the required current between them, so each one delivers less. Some batteries, such as 9V ones, are actually several cells in series.

One other thing to be aware of here (and this is a gross oversimplification, but useful nonetheless), is that what really matters as far as how much life you’ll get out of a battery is defined by the number of amp-hours. For instance, a 1 amp-hour battery can produce a current of one amp for one hour, or 2 amps for half an hour, or half an amp for two hours, etc. It’s really not quite that simple in real life, but this is a useful approximation. So if we increase the number of amp hours available in our consumer device, we can run it for longer without needing a change of batteries!

Larger batteries, such as D cells, obviously have a larger amp-hour capacity than smaller cells, such as AAA’s. So if your device runs for an hour on a two D cells, it might only run for a few moments on two AAAs, even though AAA’s have the same voltage as D cells.

Ok, now let’s consider a device that is designed to run for, say, 8 hours on two D cells. Could we make it run for the same 8 hours with a whole pile of AAA’s in parallel? Sure! But it’d be very inconvenient to have that many batteries to change. There are other issues that arise in the design of electronics that use parallel batteries as well, such as voltage reversal when one or more batteries go dead before some others.

Another fact that comes into play is the physical form factor of the device in question. For instance, surely you could run a palmtop computer for much longer from D cells than AA’s, but AA’s are thin enough to fit in the physical case.

Your question about “why not configure everything for a 9V transistor battery” can be answered by observing that 9V transistor batteries have a very low amp-hour capacity compared to other, physically larger batteries. Generally, increasing the volume of the battery increases it’s amp-hour capacity, although different types of battery technolgies have different energy densities, which one can measure in terms of amp-hours/cm^3.


Sort of related: My kid put batteries backward into a Game Boy and fied the whole thing. What happened?

I’ve always wanted to try taking two new 9v batteries and just plugging them together to see what would happen, but never had the guts (last night would have been a good time, being the 4th, heh heh). Anybody try that? Or, better yet, make a row of them, all connected in series with another row on top, then bend into a circle so that the 2 remaining posts just barely touch. How many 9v batteries would it take before you would get a continuous spark? (This is what happpens when I get a day off!) LOL

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When you hook two 9v batteries together you get nada. At least nothing exviting to watch. No sparks or anything.

Don’t take life so serious. It ain’t nohow permanent

The kid FRIED the game boy.No explanations?

Sunbear writes, “Sort of related: My kid put batteries backward into a Game Boy and fied the whole thing. What happened?”

I’m just guessing here, but I’d say what happened was that (s)he put the batteries in backwards and fried the whole thing!

If you’re asking why he did that, I have no idea :-). But it’s not inconceivable that one can fry ICs and other important bits that way.


Toymaker writes, “I’ve always wanted to try taking two new 9v batteries and just plugging them together to see”

What happens when you do something like that depends on the types of batteries in question. Every battery has what’s called an “internal resistance”, which limits its ability to deliver current to a short circuit. For a 9V battery the short circuit current probably won’t be enough to do much more than warm the battery(ies) a bit.

For other type of batteries, the short circuit current can be enourmous, and cause anything from melted internal connections to the complete destruction of the battery!


Sunbear wrote

It’s interesting how a brief question can have a long involved answer. If you want the long really involved (and most correct) answer, you’ll have to read up on semiconductor devices. I’d recommend you get really specific on MOSFETs, because I suspect most ICs in a Gameboy are MOSFETs (power considerations, you know?)

The short version is that the IC’s and printed circuit board on a gameboy are designed to have B+ (an electronicsspeak term for a generic DC voltage) on one side of the circuit and Ground or 0vdc on the other side. I mentioned MOSFET semiconductors the last paragraph. They are very sensitive to static electricity. Techs who work with them wear little grounding straps around their wrists because just a little momentary jolt of static electricity can destroy the device. Hooking up a battery backwards is more than enough to destroy the chips.

Hope this helps.

Ranger Jeff
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Sure it helps.Plus the boy now knows that a new COLOR game boy cost $70 of his saved up money.

Toymaker sed:I’ve always wanted to try taking two new 9v batteries and just plugging them together to see what would happen, but never had the guts (last night would have been a good time, being the 4th, heh heh). Anybody try that?

I have. It produces two very warm, very dead batteries.

I got the idea when I put a single 9V in my pocked with some change. About 5 minutes later I noticed a very warm sensation in my pocket. When I reached it, there was a warm batter and a hot quarter.

I wrote, “energy densities, which one can measure in terms of amp-hours/cm^3.”

Actually what I really should have said is: watt-hours/cm^3 - that’s a better measure of the energy content per unit volume of a battery.


OK, this post won’t answer the question raised, but may help someone’s pocketbook.

First of all, many “D” size batteries are nothing but a “C” size battery packed into a “D” sized outer case. How to tell the difference between one of these and a real “D”? Other than price, I have no idea. I guess you get what you pay for.

Secondly, beware the term “Heavy Duty”. That term is actually a specification. Once upon a time, Heavy Duties were stronger and lasted longer than conventional batteries. But no longer. Now, ironically, Heavy Duties are often actually weaker than conventionals --though they can still cost more.


I’ve seen that practice quite a lot with consumer D-sized NiCd rechargeables’s - they package a C or sub-C sized battery in a D cell case. The difference is usually clear when you pick one up - they’re much lighter than the real deal.


Ah…weight! So weight and price (and of course, a battery autopsy) are good indicators.

Well, I guess that since NiCads are sold by size, the practice is legal… :confused:

Yeah, it’s legal, but it’s a little unfortunate since NiCd D’s tend to be (just from memory here) only about 4-5 AH vs 20-ish for a good quality non-rechargeable. And that’s for the real ones, so if you get a sub-C in a D case, you’re probably down to less than 1 AH.

FWIW, Radio Shack, of all places, used to (maybe even still does) sell real D NiCds.



I am really shocked (har!) that there was no idiot-proofing in the Game Boy to prevent such a disaster. Almost everything I service (even the el-cheapo $10 stuff) has a fast-acting breaker or crowbar circuit in it, which forcefully blows the fuse in the event batteries are installed backwards. This used to be a big problem with people who thought they knew how to install car stereos, nowadays I doubt you could blow one up even if you tried. Electronic games are one of the few things I don’t service, but I still think that was an evil thing for [the makers of Game Boy] to have omitted this simple additional component.

Trot on over to the “diodes” thread for info on semiconductors & batteries.