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Step 1
Buy double AA batteries in bulk from chain stores. Buying batteries in bulk is the easiest way to save money.
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Step 2
Buy store brand batteries for greater savings. If the brand you buy lasts as long as you want, switch to them. If not, try another store brand. Don't buy off-brand batteries from the dollar store. These are poorly made.
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Step 3
Switch to rechargeable AA's. This takes a little more effort. Get a charger and three different sets of rechargeable AA's. You can charged four batteries at a time with most chargers. Keep all three sets charged so you'll always have some ready.
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Step 4
If your device is larger, like a calculator, see if it has a spot in the back for the a power supply. This is a small round circular plug with a metal dot in the center.
If your device can use a power supply, buy a universal power supply at Radioshack or an electronics store.
