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The difficulty that I have with NiMh batteries is that it is very difficult to tell when they are done charging, and they are less tolerant of overcharging and

The difficulty that I have with NiMh batteries is that it is very difficult to tell when they are done charging, and they are less tolerant of overcharging and "trickle charging" than the NiCad chemistries which preceded them. Most chargers will just assume that you've discharged them fully between uses, and perform a "full" charge cycle when one is plugged in, maybe with a temperature sensor to stop if they get too hot. You can't really use resting voltage as a gauge, and it's tricky to find a good charger which can reliably detect the small and brief "dip" in voltage which occurs around the time that the batteries are fully charged. They're great batteries, and I also prefer them for applications where the batteries get fully drained before being plugged in, but they can still be iffy for applications where you only discharge them briefly and want to keep them "topped up". For those applications, these days you can buy 1.5V lithium cells in AA/AAA form factors with built-in microUSB charging ports. But those are lithium-based, so you have to be careful about thermal runaway. Life is a balancing act full of compromises...

jacobush 7y ago
NiCad is the devil though but I assume you didn't advocate them, just missed a property of them.
- leggomylibro 7y ago
  Right, good point, at least NiMh batteries aren't full of cadmium.
  - durandal1 7y ago
    And has no memory which is a huge advantage.
    - aidenn0 7y ago
      NiCd memory effect is way overblown. It requires nearly identical cycles each time and has only ever been observed in high-capacity aerospace cells. [edit] Repeated overcharging can cause changing voltage curves that are (apparently) also referred to as memory effect, but NiMH cells are also prone to this.
bxparks 7y ago
The NiMH chargers that I've seen have a negative delta-V detection and a timer shutoff. I've had problems charging the Eneloops when used on devices that drain the battery too much. When they are inserted into the charger, the voltage seems to rise too quickly and and somehow confuses the charger so that it stops charging early. In those situations, I've resorted to charging those batteries twice. First time, charge for 5-10 minutes to raise their voltage. Then remove and reinsert the batteries to charge a second time using a more normal voltage curve. Maybe it's a quirk of my charger. I didn't know about lithium AA/AAA rechargeable batteries. Interesting. I see that most are rated at 1200-1500mAh (AA) and 400-500mAh (AAA). These are only a little over 1/2 the capacity of the NiMH that I normally use. I guess the charging circuitry takes up room in the battery.
- leggomylibro 7y ago
  Got any charger recommendations? :) And yeah, the lithium AA/AAAs were news to me too. I learned about them when I got a headlamp that could either take 3 AAA batteries or a same-sized lithium battery with +/- contacts in the right places. I think the single-cell ones include a buck converter along with the charging circuit, which probably cuts down on the space they can devote to the battery itself.
  - bxparks 7y ago
    Yup, it's old but I use this Titanium Smart Fast 8 Bay AA/AAA charger (https://www.amazon.com/gp/product/B0035HCTLS https://www.amazon.com/gp/product/B0035HCTLS). The manual states that it has negative delta-V and timer shutoff. One of the Amazon reviewers mentions a problem with deeply discharged batteries, similar to what I've seen where I need to charge the battery twice. By the way, this situation happens mostly on my motion-activated staircase LED lights which take 4 x AA. That thing is amazing because it works until 3 x AA are essentially dead and only 1 x AA is giving out power. For most of my other devices, the device stops working before the battery voltage becomes that low.

jacobush 7y ago

NiCad is the devil though but I assume you didn't advocate them, just missed a property of them.

leggomylibro 7y ago
Right, good point, at least NiMh batteries aren't full of cadmium.
- durandal1 7y ago
  And has no memory which is a huge advantage.
  - aidenn0 7y ago
    NiCd memory effect is way overblown. It requires nearly identical cycles each time and has only ever been observed in high-capacity aerospace cells. [edit] Repeated overcharging can cause changing voltage curves that are (apparently) also referred to as memory effect, but NiMH cells are also prone to this.

bxparks 7y ago

The NiMH chargers that I've seen have a negative delta-V detection and a timer shutoff. I've had problems charging the Eneloops when used on devices that drain the battery too much. When they are inserted into the charger, the voltage seems to rise too quickly and and somehow confuses the charger so that it stops charging early. In those situations, I've resorted to charging those batteries twice. First time, charge for 5-10 minutes to raise their voltage. Then remove and reinsert the batteries to charge a second time using a more normal voltage curve. Maybe it's a quirk of my charger. I didn't know about lithium AA/AAA rechargeable batteries. Interesting. I see that most are rated at 1200-1500mAh (AA) and 400-500mAh (AAA). These are only a little over 1/2 the capacity of the NiMH that I normally use. I guess the charging circuitry takes up room in the battery.

leggomylibro 7y ago
Got any charger recommendations? :) And yeah, the lithium AA/AAAs were news to me too. I learned about them when I got a headlamp that could either take 3 AAA batteries or a same-sized lithium battery with +/- contacts in the right places. I think the single-cell ones include a buck converter along with the charging circuit, which probably cuts down on the space they can devote to the battery itself.
- bxparks 7y ago
  Yup, it's old but I use this Titanium Smart Fast 8 Bay AA/AAA charger (https://www.amazon.com/gp/product/B0035HCTLS https://www.amazon.com/gp/product/B0035HCTLS). The manual states that it has negative delta-V and timer shutoff. One of the Amazon reviewers mentions a problem with deeply discharged batteries, similar to what I've seen where I need to charge the battery twice. By the way, this situation happens mostly on my motion-activated staircase LED lights which take 4 x AA. That thing is amazing because it works until 3 x AA are essentially dead and only 1 x AA is giving out power. For most of my other devices, the device stops working before the battery voltage becomes that low.