Any reason NOT to use NiMH rechargeables??

[highdesert]

Greetings -

Thinking about getting some sets (AA and C) of NiMH batteries and charger from Thomas Distributing to use in UK, Princeton and Pelican lights, some LED, some xenon. Is there any reason these batteries would not perform well? If you go to the various sites of the manufacturers, they talk about using alkaline or nicad. Any thoughts??

 

[Capt.Rich]

I cant see any disadvantage to using them. Thye are generally designed for use in high current demand devices.
One of the downsides to those type rechargeables is that they will lose there charge simply sitting around doing nothing. I believe the last technical piece I read said that they can lose 5-10 percent of there charge per week.

 

[ReefHound]

Yeah, there are some negatives. They lose their charge over time so they are not recommended for your backup light. They maintain a flat voltage curve meaning they output full voltage almost until the end then drop off rapidly. This is good and bad, they won't gradually dim like alkalines so you maintain light output but you also aren't aware that they are getting weak and need replacing/recharging. That's another reason not to use in your backup. I've also heard they are more "reactive" with seawater contact so if a light floods you want to get the batteries out of there quickly. All that said, I use them in lights and cameras all the time.

 

[Meng_Tze]

As long as you charge them before the dive you should be okay. NiMH does not suffer from memory effect as NiCad does, so topping up just before a dive is not an issue. Just don't let them go dry between two dives. When using backup lights, one should always make sure that their burntime exceeds the dive time. This does not preclude usage of NiMH batteries, just that you need to make sure that the 'knee' in the discharge curve happens to be further out in time than the dive time. So if my backup light runs for 4 hrs before the knee in the discharge, I would be very comfortable doing a 3 hours or less dive on the batteries.

 

[highdesert]

Thanks for the tips, everyone. Been doing some reading about pros/cons of NiCad vs. NiMH today, and it seems the conclusion for me is that since I always top up batteries daily, I should be good with NiMH, using a smart charger. Am I right in that respect?

 

[BMW]

I use NiMH in my UK C8 eLED light. When the batteries are fully charged the light is fine.

However, consider that this (and other) lights are designed for alkaline cells which are 1.5V each. So 8 cells in series should be 12V and the light was designed for 12V and will appear dim at 9V.

NiHM and NiCad cells are 1.2V each, so 8 cells in series are 9.6V. The light will still appear dim when the batteries hit 9V, which will occur much sooner than if you were using alkaline.

Apart from having to charge more frequently than I originally expected, I have had great results from my light.

My recommendation for the manufacturers would be to design the lights for NiHM/NiCad in the first place. E.g. design a C10-nimh that takes 10 NiMH cells (or a custom battery pack) for 10x1.2 = 12V.

Just my 0.02

 

[Meng_Tze]

Thanks for the tips, everyone. Been doing some reading about pros/cons of NiCad vs. NiMH today, and it seems the conclusion for me is that since I always top up batteries daily, I should be good with NiMH, using a smart charger. Am I right in that respect?

Do you top up daily but do not use the batteries daily? If this is the case, you may be effectively shortening their life.

This is what I do: If I would dive tomorrow, I would charge batteries today. Put them in the light and go diving. When I come back, I just store the batteries in a cool place (walk in closet in the house). If I dive next saturday, I would just top up on next Friday.

If however I would have used the batteries beyond say a 70% discharge, I would top up when I came back from my first dive.

This way you minimize topping up/charging; taking away from the battery life while avoiding internal damage by not storing them without a charge, or a low charge.

If you dive regularly or use the batteries for primary lights, then this will work. If you use them for backup lights, you may have to adjust the schedule to avoid the batteries self discharging.

YMMV though

 

[highdesert]

Do you top up daily but do not use the batteries daily? If this is the case, you may be effectively shortening their life.

This is what I do: If I would dive tomorrow, I would charge batteries today. Put them in the light and go diving. When I come back, I just store the batteries in a cool place (walk in closet in the house). If I dive next saturday, I would just top up on next Friday.

YMMV though

After doing some reading yesterday, my "topping off" days are essentially over. I got the impression from reading, though, that NiMH were the most resistant to that practice.

I don't understand, in your example, the difference between recharging right after the previous dive, or a week later right before the next one. Are both not the same?

I also learned yesterday that after sitting for 3 months, the NiCad battery packs in our UK lights (LED) will burn brightly for 4 hours on their residual charge. With that kind of life, maybe we just need to learn how to manage the charging cycle on those without shortening their life too uch.

 

[jtivat]

I use NiMH in my UK C8 eLED light. When the batteries are fully charged the light is fine.

However, consider that this (and other) lights are designed for alkaline cells which are 1.5V each. So 8 cells in series should be 12V and the light was designed for 12V and will appear dim at 9V.

NiHM and NiCad cells are 1.2V each, so 8 cells in series are 9.6V. The light will still appear dim when the batteries hit 9V, which will occur much sooner than if you were using alkaline.

Apart from having to charge more frequently than I originally expected, I have had great results from my light.

My recommendation for the manufacturers would be to design the lights for NiHM/NiCad in the first place. E.g. design a C10-nimh that takes 10 NiMH cells (or a custom battery pack) for 10x1.2 = 12V.

Just my 0.02

Yes but under load the alkaline batteries voltage will drop much more than NiMH batteries will. So under load the voltage will be much closer and even more so in high draw lights.

 

[highdesert]

From FAQ's at http://www.greenbatteries.com/nibafa.html


"Even though alkaline batteries are rated at a nominal 1.5 volts, they only deliver 1.5 volts when they are fully charged. As they begin to discharge the voltage of alkaline batteries continuously drops. In fact, over the course of their discharge, alkaline batteries actually average about 1.2 volts. That's very close to the 1.2 volts of a NiMH battery. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volts. NiMH batteries stay at about 1.2 volts for most of their discharge cycle."

However, my personal interest is in NiCad vs NiMH; I really want to leave behind the issue of depleted alakalines piling up (though I understand there are disposal issues to be dealt with, particularly with NiCad).