Like most people, you probably have a number of devices that run on battery power. Could be clocks, cameras, portable stereos, flashlights, remote controls, ... Like most people, you probably buy your Duracell or Energizer batteries at the store and throw them away when they're spent, right?
That's exactly what the battery companies want you to do: keep buying more and more batteries. More profit for them.
But there is an alternative. Many of your electronic devices may already have customized versions of this built in - many digital cameras, laptops, and portable music players have this: rechargeable batteries.
Rechargeables are not just for custom applications. They make rechargeables in nearly all standard battery sizes: AA, AAA, 9-volt, C, D. They typically last longer than standard alkaline batteries (the throw-away kind) and can be recharged about 500-1000 times. Let's do some math:
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A pack of 4 AA batteries costs $2.74 at Wal-Mart. Let's say you have a portable CD player that goes through 2 AAs every 3 days. Thus you buy 5 packs every month:
$13.70/month or $164.40/year
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A charger that charges 4 AA or AAA rechargeable batteries in 1 hour will cost you anywhere from $20-$30. We'll assume worst case: $30.00.
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A 4-pack of rechargeable AA batteries will run you about $10.00. Those batteries will recharge about 500-1000 times, so we'll assume the worst case, or 500 recharge cycles.
Let's look at your total spent, month by month:
| Month | Disposable | Rechargeable |
|---|---|---|
| 1 | $13.70 | $40.00 |
| 2 | $27.40 | $40.00 |
| 3 | $41.10 | $40.00 |
| 4 | $54.80 | $40.00 |
| 5 | $68.50 | $40.00 |
| 6 | $82.20 | $40.00 |
| 7 | $95.90 | $40.00 |
| 8 | $109.60 | $40.00 |
| 9 | $123.30 | $40.00 |
| 10 | $137.00 | $40.00 |
| 11 | $150.70 | $40.00 |
| 12 | $164.40 | $40.00 |
| . . . | ||
| 80 | $1,096.00 | $40.00 |
After 80 months, you'll have recharged the batteries 480 times, or about half of their maximum recharge cycles. If you were unlucky, they may be near their end of life, in which case you saved "only" about $1,000. For one application!
Update:DeathAwaitsU correctly points out that you also have to consider the cost of recharging the batteries. The most expensive electricity in my market costs about $0.22 per kilowatt-hour. Most of it's much less, but this rate kicks in when you've gone over your baseline energy usage for the month. AA batteries put out 1.2 volts of electricity. And a typical rechargeable AA stores about 2500 milliamp-hours, or mAh, of electrical charge (see below).
Now, for a physics lesson.
- Electricity from the power company is measured in kilowatt-hours (kWh), which is a unit of energy.
- A watt is a unit of power, which is energy per unit time. 1 watt = 1 joule per second, or 1 W = 1 J/s
- A coulomb (C) is a measure of electrical charge.
- An ampere (A) is a measure of electrical current flowing through something, or number of coulombs per second. 1 A = 1 C/s
- A volt is a measure of electrical potential, or energy per unit charge. 1 V = 1 J/C
Time to put it all together:
($0.22 / kWh) * (1 kW / 1000 W) = $0.00022 / Wh
($0.00022 / Wh) * (1 h / 3600 s) = $0.00000006111 / Ws
1 Ws = 1 (J/s)s = 1 J
Energy cost = $0.00000006111 per Joule
Energy stored in 4 charged AA batteries:
4 * 2500 mAh * 1.2 V = 10000 mAh * 1.2 V = 10 Ah * 1.2 V
10 Ah * (3600 s / h) * 1.2 J/C = 36000 As * 1.2 J/C
36000 As * 1.2 J/C = 36000 C * 1.2 J/C = 43,200 Joules
Multiplying by the energy cost per Joule, we get:
43,200 J * $0.00000006111 / J = $0.0026 to charge 4 batteries - less than a third of a cent.
After 480 charge cycles, we pay about a dollar for the electricity to charge the batteries.
Use rechargeables for everything that needs batteries, and you can save quite a bit more. Plus you help save the environment by throwing away far fewer spent batteries! The battery companies don't want you to know this - that's why they quietly make rechargeables but never advertise them.
Personally, I have a few sets of AAAs and several sets of AAs on hand. I use them in everything from my digital camera (which got me started on rechargeables 5 years ago) to remote controls, clocks, and more.
You can buy rechargeables at most stores that sell disposable batteries, and they also sell chargers too. However those chargers tend to be lower quality and will often cut short the number of usable charge cycles you get out of your batteries. I've had good luck with Maha chargers, which can be had at Thomas Distributing (I personally recommend them).
For batteries, look at the total charge rating, which is normally expressed in mAh - milliamp-hours. 2500 mAh is a pretty good capacity for AA rechargeables these days, and it means one battery can output an electrical current of 1 milliamp for 2500 hours. Or 2500 milliamps for 1 hour.
When you do the math, this is the biggest no-brainer in the history of mankind!
