Newbie Question, NiMH batteries in flashlights

[Saaby]

Yes and no. Yes you can do it, yes it might last longer but that all depends on what kind of light it is, what kind of light is it?

NiMh have less voltage when fully charged then fresh alkenlines that is true, but they also have a flatter discharge curve, meaning that after using regular batteries for only a short time, they'll have lower voltage then NiMh. Maybe another friendly CPF member can post a graph.

I personally don't like to use NiMh in my torches because they have a high self discharge rate and if you discharge them too low is can dammage the battery, but many others use them with no problems. Also, in some cases it's better to use NiMh because of the lower voltage. In some of the home made flashlights around here it's better for the LED to be run at a lower voltage, but that isn't really the case with lights bought at the store.

 

[Ratso]

Thanks for the reply,

I have a cheap Eveready 4AA but it is very bright. I wouldn't mind a drop in voltage since it is bright enough anyways. I would like a longer run time and (as you mentioned) flatter discharge curve so it will stay brighter longer.

2 more questions:


What is the mAh of an alkaline vs. a NiMh (+ heavy duty just for comparison)?

Will NiCads work too?

 

[Ratso]

Oops, I just thought of another question:

What about Lithium AA batteries. I believe they are 3volts, what if I switch the bulb to say a 12 volt bulb will that work too?

 

[Brock]

Alkaline AA's run about 2700mA, and good NiMH's are about 1600mA to 1800mA. The problem is as noted before, when an alkaline battery is down to 1/4 full it is at about .6v while a NiMH at 1/4 full is up at 1v or so. So alkalines often appear "dead" after about 1400mA. Older carbon zinc or "heavy duty" batteries are typically about 1000mA, but again they appear dead after about 500mA.

Ni-Cad's are similar to NiMH, but don't have the capacity of NiMH; they typically run about 800mA to 1000mA. The advantage of Ni-Cad is they are better in hi-drain situations.

Li AA cells are 1.5 to 1.7v new and will work fin in most lights. They run about 2800mA (the highest of the group) and they will hold a useable voltage right to the bitter end, so you get the full 2800mA out of them. They are the best choice, but also the most expensive in the long run. They also hold their charge the longest (over 10 years to 90% of full), while alkaline is 2 years and NiMH and NiCad are about 2 weeks.

 

[Saaby]

The 3V lithiums you were asked about are not AAs. I believe you are confusing the new lithium AA batteries and CR123 latteries, which are also lithium. As mentioned above, the lithium AAs are 1.5-1.7 V, the CR123 batteries, which are the kind used in many cameras now days, are 3V.

 

[lemlux]

AA cells and A cells are each 50.5 mm long.

AA cells have a diameter of 15.2 mm
A cells have a diameter of 17mm

The CR123 is a 2/3 A cell.

It is 2/3 of 50.5 mm long or 34 mm.

 

[sunspot]

There are 3.6v lithium AA's. They are for low load not high drain.

 

[Ratso]

Can I use rechargeable 1.2v NiMH batteries in flashlights that require 1.5v alkaline?

Will it diliver less power but last longer or what?