Rechargeable NiMH Batteries
At one point, I rid myself of all disposable battery powered devices except for my entertainment system remote controls. That was before Wyatt reached an age where every toy seems to require batteries and before my favorite tech gadgets of the moment became things reliant on AA batteries. Both the Edirol R-1 I use daily for portable recording and the similar Marantz PMD660 are powered by AA batteries. I hate the idea of buying disposable batteries and throwing them out. They aren't cheap in the first place, they aren't particularly good for the environment and depending on which disposables you buy, batteries don't necessarily have a long life. As a result, I've been doing some serious research into which NiMH batteries offer the best rechargeable alternative to disposables, with the biggest attention paid to finding the longest lifespan batteries for my portable devices. What I've found is all rechargeable NiMh batteries are not created equal.
At my house, I currently have three different flavors of AA NiMH batteries. Some of them came from Radio Shack. Some are Energizer NiMH rechargeable batteries and a few are from aftermarket camera part maker Lenmar. Each brand came at a time when they were the best option available for my immediate need, even though there is a key difference between each battery brand. In order for a rechargeable battery to qualify as AA, it must be of the appropriate shape and deliver 1.2 Volts (alkaline disposables are rated at 1.5 Volts but typically average 1.2 Volts over their life). There seems to be no requirement regarding how many milliamp hours (mAh) a particular rechargeable will be rated for.
Across my three different battery brands, I have three different mAh ratings. The Radio Shack batteries provide 1800mAh, the Lenmar is rated at 2300mAh and the Energizer offers the most power at 2500mAh. For continuous use devices, like my Edirol R-1, a higher mAh rating is definitely desirable for long recording periods, because I can do more field recording on a single charge. In practice, I've gotten at least 25% more battery life by using the 2500mAh Energizer batteries compared to the 1800mAh Radio Shack batteries. The bottom line here is, before you buy, check the package to make sure you're getting the best battery for the job. The price difference between the three batteries mentioned here is negligible. The performance of each does show a marked difference in terms of the amount of recording I can do on a single charge.
For functions that require larger bursts of power, like taking a digital photo, recording audio with a solid state recorder or even providing a continuous light source with a flashlight, NiMH batteries will generally last longer than disposable alkaline alternatives. They may need to be recharged more frequently than a disposable would need to be replaced in devices that use very little power like a television remote control. Especially in warm areas, NiMH batteries are more likely to bleed power than alkaline disposables, so consider the function of the battery before making a decision about which type of battery you want to use.
Keeping track of battery life with NiMH batteries is tricky. The general litmus test for a batteries remaining lifespan is the voltage it delivers. For disposable alkaline batteries, this starts at around 1.5 Volts, drops to around 1.25 Volts at 50% capacity and bottoms out around 1.0 Volts when the battery is almost completely drained. Assessing battery life is reasonable easy by checking the voltage against where it is in this lifecycle. NiMH batteries tend to maintain a consistent 1.2 Volts until they drain, which means if your digital camera warning light comes on when you're using a NiMH rechargeable, you better believe the battery is almost dead. Li-ion batteries, which are more commonly found powering cameras that ship with rechargeable batteries, are more likely to present a low battery false positive, which means you have longer until the battery dies than the camera thinks you do.