After hours and HOURS, weeks and WEEKS (ETC!) of running flashlights and measuring battery strengths (every five hours of use), Emily is FINALLY done with her science project:
After 335 hours, I can tell you that Panasonic brand batteries were the only brand still running in the refrigerator, and that Panasonic and Sunbeam brands were the only ones still running at room temperature. Who knew they'd last that long?? NOT US!!!
I can also tell you that the batteries lost SIGNIFICANT amounts of strength in just the first 5 hours of use, and then lost it much more slowly after that (you can see the huge drop on the far left of each of the two line graphs in the middle of her display board).
I can also tell you that batteries recharge themselves quite a lot in the hours they are not in use (hence the VERY unexpected up and down zig-zaggy line graphs she ended up with). I expected she would see a steady decline in battery strength as the hours passed, and that she'd be able to make some predictions about which brands were getting ready to die based on their low strength. NOPE! While there IS a definite downward trend to the graph, it's pretty much entirely an up/down/up/down pattern, and they all stayed within a very similar range of strength.
I can also tell you that when a flashlight uses more than one battery, it seems to drain one battery much more than the others (when a flashlight would die out, she would test all three batteries, and each time, one battery was very low, while the other two were still within the range of flashlights that were still working), which leads me to believe you could possibly get more life out of your batteries by rotating them within the flashlight from time to tme, but we didn't test that to be sure...
I can tell you that the Panasonic and Sunbeam batteries we used were purchased from the Dollar Tree. Nothing fancy or expensive, nothing you see commercials for (though to be fair, Energizer lasted the second longest in the fridge, and while it didn't last overly long at room temperature, it's possible it was a faulty flashlight because it died out with pretty high voltage readings...).
This project turned out to be much more labor intensive than I would have predicted. This was mostly because of measuring all the battery strengths every five hours, and then having to enter the information into the computer to make the lines graphs... It also got tricky finding enough time to run the batteries, and also time it out so she'd be home at the five hour mark. Emily was THRILLED when the project was finally over. We already have a fun idea for next year, and I can safely say it shouldn't take 335 hours!! *grin*