Originally Posted By: Eugene

The self discharge of NiMH is about the same as low self discharge NiMH so no advantage there.


I don't understand what you are saying here. The self discharge rate of NiMH is much higher than lithium ion.

Quote:
They do weigh less but in anything that uses them in a pack such as GPS or radio you still need a special charger so the weight savings is lost there.


Again, I don't understand. If you use any type of rechargeable battery, you need to make provisions for charging in the field, or providing spares. This would be the same for NiMH or lithium ion.

Lithium ion doesn't work for many devices due to the difference in voltage (witness GPS) and I'm not suggesting you go crazy trying to make it work.

Although, I will point out that *if* you try to take a generic external battery pack, lithium ion is going to be a big win if you are carrying it due to the lighter weight.

example

Quote:
Then figure in the cost of replacing the battery pack or cells about twice as often as NiMH even if they are not used since they deteriorate with age.


I suppose. It hasn't been my experience, FWIW. Even with a decent, independent cell charger and effort doing charge management, NiMH has always been a bit of work, and I've always had cells go bad in what seems like a short period of time. Contrast that with the handful of 18650s I swap out in my EDC light which I use all the time which have never been problematic and I have yet to have one go bad.

It has been charge, use, repeat.

The original poster talked about use in a flashlight, so as a random comparison here are two total flashlight solutions (light + two sets of batteries + charger):

Example AA Solution
Quote:

Fenix LD20 Q5 flashlight (2xAA), $63
* levels: 9, 47, 94 or 180 lumens
1 x Maha MH-C9000 charger = $49
4 x Sanyo 2700MAH batteries = 13
Total: $125

(battery/charger source - thomasdistributing.com)


Example Lithium Ion solution
Quote:

1 x Fenix TA21 flashlight (1x18650 or 2x123A), $98
* levels: 4, 35, 80, 160 or 225 lumens
2 x LG 18650 3.7V 2600MAH = $20.00
1 x TL-100 Universal Li-Ion Charger = $15
Total: $133

(battery/charger source - batteryjunction.com)


(source for both lights - fenix-store.com)

Pretty close price-wise IMO.

I'm not saying lithium ion is the answer for everything, but I think it has compelling cases. And actually, it pretty well excels in flashlights (use specifically mentioned by the original poster).

-john


Edited by JohnN (07/24/09 12:01 AM)