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05-19-2009, 01:18 PM   #13
Quension
Senior Member




Eneloops are still just NiMH batteries and can be charged by any NiMH charger.

The two most important things you want in a charger is the ability to charge cells individually/independently, and the ability to stop when a battery is full. You should be able to put one battery in any slot and have it be charged until it's full, at which time the charger will stop. A less intelligent charger will only charge 2 or 4 batteries at a time, which can cause problems at both ends of the spectrum: a single battery may be overcharged, significantly shortening its life; a single battery may be undercharged, and when you use it in a device with other fully charged batteries it may become "too empty" first and be permanently damaged by the others that still have a charge. An even less intelligent charger will use a timer instead of sensing when a battery is full, pretty much guaranteeing it will be overcharged. A just plain stupid charger will never stop and is a fire hazard; it boggles the mind that these pieces of junk are still sold.

Rapid chargers wear out batteries faster. Advice for the "right" charge rate varies, but in general anything that charges a battery in less than about 1 hour is considered harmful, 2 hours is considered okay but not great, and 4 hours seems to be a good time. Many chargers are sold by time, but that isn't an accurate rating, since battery capacity varies. Eneloops have a capacity of 2000mAh (milliamp-hours). If you charge one at a rate of 2000mA, then it will take 1 hour to charge; 1000mA will take 2 hours, etc. Look for the charging current and battery capacity numbers and do the math yourself to see how long it will take.

A related issue is that charging them fast makes them heat up, so there's a greater risk of fire if something goes wrong. Smart rapid chargers have temperature sensors and will cut power if a battery gets too hot.

While NiMH batteries don't have a "memory" per se, they do decrease in capacity over time. Smarter chargers have a "refresh" function, which completely discharges and then charges a battery repeatedly until it has regained maximum capacity. There are many stories of this process restoring tired batteries to a usable state again (albeit not quite as good as brand new). Given a gentle charge rate, this is something that can take several days to complete.

Smarter chargers also have a function to discharge a battery completely before charging it again normally. I have not seen any concrete information about whether this keeps batteries at top capacity longer compared to normal use and a plain charge, but presumably it has some benefit.

I like the LaCross BC-700 and BC-900 as advanced chargers. Armed with some basic knowledge, they're straightforward to use, and fairly smart.

One smart charger with no advanced functionality is the Duracell CEF23 (CEF23DX2 / CEF23DX4). It only charges, no discharge or refresh functionality, but it's intelligent enough to handle batteries independently, is gentle, and has a temperature safety. It's also cheap and simple.

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