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Granted, half-charging your rechargeables repeatedly can be damaging for them.

Sony’s “Stamina” AAs are pretty good, too.

And you’re right, Troy: I have a fistful of Duracell/Energizer AAs and AAAs. They’re great for about 25 cycles and and blow chunks after that.

–Mark

They MUST increase the charge current. NiMH cells don’t trickle-charge well. In fact, most mfg’s like sanyo and gold peak actively discourage trickle charging in favor of a dV/t terminated fast charge.

Also, from what i’ve seen, most products that take “D” cells, and there aren’t many anymore, require 4 to 8 batteries.

Four tenergy D batteries go for about 50 dollars. Not many people are smart enough to realize that it’s not a bad deal, and a good portion of the rest simply can’t afford it. Not many people are willing to put 50 bucks in batteries in a flashlight.

Hell, “D” batteries aren’t even common for OEM purposes. Even EV’s and stuff use SubC.

Energizer D rechargeables are really mostly just legacy support.

Battery chargers work by providing a slightly higher voltage than a discharged battery would have. That essentially forces energy into the battery, which stores it up for use later. The problem is that you can’t just connect, say, 1.5V to a 1.2V cell, because the cell will ingest energy at the highest rate the source can provide it. That sounds like a recipe for a nice, fast, charge, but the process has the side effect of producing heat, too much of which will damage the battery.

To get around that problem, chargers are built with a circuit that limits the amount of current to what’s safe for the cell. Most battery chemistries charge best in the neighborhood of 10% of their capacity. In other words, a 2000 mAh AA cell charges best at a rate of about 200 mA, and a 9000 mAh D cell does best at a rate of 900 mA. (There are high-capacity C and D cells available from battery supply houses. They run about $25 each.) You can charge the D cell in a low-rate charger designed for AAs, but it’s going to take more than four times as long to get a full charge. You can’t do the opposite, because a high-rate charger that thinks it’s charging Cs or Ds will happily feed a AA more current than it can handle safely. You may have noticed that the 15-minute rapid chargers that have appeared in the last few years have fans in them. That allows a higher charge rate by getting the heat away from the batteries.

Energizer’s claim about the economics of Cs and Ds is correct: the market just isn’t there for them. AAs and AAAs are far and away in the majority of batteries sold, so the economies of scale in manufacturing them are much greater. Cs and Ds are relegated mostly to flashlights, where the self-discharge rates on rechargeables make alkalines a better choice if you expect them to work after a year of being under the seat of your car.

–Mark

Reply to the “let consumers decide” notion:
Consumers that buy brand name products do so via the notion that a brand name product (mainstream Wal-Mart stock) is trustworthy and better for all reasons meriting a high price. I doubt they are going to shop around just before Christmas for a set of rechargeable D cell batteries for a few hours and have them shipped when they could just snag a set at Wal-Mart or Best Buy. It’s not entirely fair to push blame onto a consumer. I’ve always hated off brand batteries for short life and leakage, and usually buy brand name batteries despite the price with the notion that spending more will result in better life span and quality, but these batteries do not honor that.