Why Do 9v Batteries Suck?

September 9, 2008 1:29 PM

So the modern practical uses for these are in guitar effects, alarm clocks, and smoke detectors. leave your effects on and they die in a couple of hours. as a backup to your alarm clock, it dies in four or five hours (not even powering the LCD). i have no idea how long these things last in a smoke detector, but my guess is the next housefire and i'm a dead man. why do these batteries suck so bad? why do we still use them? why hasn't science come up with anything better?
posted by camdan to technology (18 comments total)

Modern guitar effects are using some fairly substantial computing power compared to older effects. I have a distortion pedal that I built in 1983 from a Craig ANderton design (Tube Sound Fuzz), that uses a single CMOS chip in it. I've changed the battery twice.
posted by plinth at 1:38 PM on September 9, 2008

Open a 9v up and it's just AAA batteries in series. You could probably get a lithium 9v that lasted longer.
posted by acro at 1:57 PM on September 9, 2008

Retraction...in parallel, and they're actually 'AAAA' batteries.
posted by acro at 2:00 PM on September 9, 2008 [2 favorites]

acro - yes i've seen that hack before. but how often do you have loads of 9v batteries on you and not a AAA/AA in sight? not in my highschool calculus class, that's for sure.
posted by camdan at 2:13 PM on September 9, 2008

why do these batteries suck so bad?

Because to get 9V, you need six 1.5V cells, which means the cells are tiny (you have to be able to fit six of them inside a 9V battery) compared to even an AA battery, which means they do not contain much power and are exhausted rapidly.

Basically, a 9V battery gives you a higher voltage for a shorter duration. Duration is the trade-off for the greater voltage.
posted by -harlequin- at 2:23 PM on September 9, 2008

It's a tradeoff between battery life and compactness -- using the quad-A cells in parallel means that you have the effective battery life of a single quad-A cell (at 1.5V, as -harlequin- mentions). Traditional battery technologies don't produce high enough voltages to use a single cell in that format -- Lithium-based batteries produce somewhere over 3V/cell and have a high energy density, which is why they last longer in the same form factor (more energy per cell and fewer cells required in the same space).

Realistically, there are hard upper limits to cell-based battery technology that explain why nothing better has been generated as a replacement for a small 9V source -- the absolute limit for a simple reduction cell is somewhere below 6V, and that involves dangerous materials that wouldn't be used in a consumer battery.
posted by j.edwards at 2:31 PM on September 9, 2008

why hasn't science come up with anything better?

That's an involved question that I will bypass by suggesting people aren't sufficiently bothered to part with the extra $$ for what is better. But if you look, you'll find things.

As acro mentioned, I imagine there are lithium-based 9V cells, but if so, they will likely be a specialized order and not cheap.

I myself have a little adapter that takes 1.5V from a single AA cell, and converts it to 9V, and which is small enough that both the AA cell and the adapter can fit in a 9V battery compartment. This is cheaper than using disposable 9V batteries, since AA's are a single cell and thus much cheaper per watt-hour than 9V batteries.
No doubt you can buy these adapters as kits, if not finished products, but I can't find a link to mine, as it's no-longer in production.
posted by -harlequin- at 2:34 PM on September 9, 2008

@ acro, I think that you were right the first time with the AAAA's in series as opposed to parallel. If they were in parallel, you'd still have 1.5 V but a lot more available current. Since they're in series, the voltage adds up and you have 6 * 1.5V for 9V but with the same amount of current available as in a single battery.
posted by royalchinook at 2:39 PM on September 9, 2008

why hasn't science come up with anything better?

Because it's a fundamentally difficult problem. It resides in the realm that engineers refer to as "non-trivial".

Believe me, a lot of people are looking.
posted by Class Goat at 2:41 PM on September 9, 2008

I've found that on average they'll last in a smoke detector for around 2 years, before the low battery beep kicks in. As for alarm clocks, my Oregon Scientific clock has been running on the same pair of AA cells since about 2002. 9V batteries are available as NiMH rechargeables, which is what I use for my ultrasonic cat-repeller; one charge lasts about a month, so I'm not particularly upset.
posted by le morte de bea arthur at 2:44 PM on September 9, 2008

You could use Ultralife lithium 9V batteries, which have several times the energy capacity of alkaline batteries, but cost about six bucks each.
posted by JackFlash at 2:46 PM on September 9, 2008

If your smoke detector bothers you, it is recommended to change the batteries every time we change to and from daylight saving time (this one says once a year, I've also heard at both time changes).

Also, your smoke detector should warn you when the battery is dying (you'll hear a chirp once in a while and spend a couple of days trying to figure out where it is coming from before realizing that the battery in your smoke detector is going)
posted by dforemsky at 2:47 PM on September 9, 2008

We have hard wired smoke detectors, that use a 9V as a backup.
posted by fixedgear at 5:18 PM on September 9, 2008

science has come up with AC adaptors
posted by canoehead at 6:17 PM on September 9, 2008

this has been an informed and insightful debate. thank you for your participation.
posted by camdan at 6:32 PM on September 9, 2008

Realize you've pretty much closed this off, but I'm going to chime in anyway. As other have alluded to, the problem you're talking about is one that thousands of engineers around the world are at this moment trying to solve. It's the issue that makes electric and hybrid cars very difficult, for example.

The governing factor here is energy density, the amount of energy that can be extracted from a pound of a given material or chemical process. If you look at that chart, the reason electric cars are tricky is instantly clear: Gasoline is over 200x as energy dense as a NiMH battery, so if you just go swapping batteries for your gas tank, your 20 gallons of gas needs to be replaced with 24,000 pounds of NiMH batteries if you want to maintain the same range, performance, etc. On the other hand, we put up with batteries because they can do the one cool thing gas can't -- refill themselves from any other available energy source like, say, braking.

That's more or less the crux of our entire energy problem right now. We've had this incredibly energy-dense material all over the place for the entire span of industrial civilization. Everything we've ever invented, batteries included, pales in comparison. Big surprise to me on the chart is that gas beats Hydrazine, which we use in spacecraft. (Note that burning hydrogen is the only thing short of nuclear power that beats petroleum, which explains why folks went hydrogen-crazy a few years ago -- you just have to keep reminding yourself that H is itself a battery of sorts, and you still have to get that energy from somewhere.)
posted by range at 7:42 PM on September 9, 2008

well i think this settles the presidential debate - first candidate who can power my mini with a (new-and-improved, non-crappy) 9v battery gets my vote. even if she's busy hunting moose knuckles in the wilds of alaska in her bikini and hot-teacher glasses most of the time.
posted by camdan at 6:16 AM on September 10, 2008

i know we finished this off, but here's a good link about the stagnation of battery development -

i can has power?
posted by camdan at 12:42 AM on September 17, 2008