Self-Discharge rates: Alk vs. NiMH

[Buck91]

Well, I receently found some Ultralast AAA NiMH batteries laying around, NIB, and have been considering throwing them into...something. Most likely my bicycle tail light. They claim to have a larger storage compacity, and wiki says a self-discharge rate of .5-1%/day after the first day (at 5-10%/day) is typical.

What I do not know is how this compares to alkies. I've used alkies all my life, in all types of temps and conditions, but never NiMH (at least not enough to draw an accurate empirical comparision). Does anybody have any tech data on alkaline battery self-discharge rates?

 

[Marduke]

NiMH typically loose 30% charge per month unless you're talking about the newer low self discharge cells like Eneloop or Rayovac Hybrid. You'll want to compare the discharge rates at 20 degrees C for room temperature.

http://data.energizer.com/PDFs/temperat.pdf

 

[Fallingwater]

Alkalines have no significant self-discharge.

 

[Marduke]

Alkalines have no significant self-discharge.

Umm... that's why they have an expiration date. They discharge to 80% at 7 years when stored at room temperature. Check the "Projected Service Maintenance" charts.

 

[Buck91]

30%/month really isn't too bad, thanks for the advice.

 

[itguy07]

Umm... that's why they have an expiration date. They discharge to 80% at 7 years when stored at room temperature. Check the "Projected Service Maintenance" charts.

I've found the expiration date to be pretty much meaningless:

2x Kirkland AA, Exp 2003 - lasting a very long time in a AA Maglite with a 1w Nite-ize. I'd say I've gotten at least 3 hours out of them so far with little signs of stopping.

3x Duracell D, Exp 2003 - lasted in a MagLite for a while and were in that same lite with a TerraLux upgrade. Just tossed them a week ago. I'd guess about 3-4 hours on them with the LED, including a 1-1.5 hr. lawn mowing session one night.

2x Kirkland AA, Exp 2003 - lasting pretty decently in a Casio pocket TV.

I've been extremely surprised how long these 4+ year old batteries have done. Until recently, they have been in storage for a long while.

 

[Bullzeyebill]

If you keep discharge between 100-300mA's the alkalines will do very well. With the newer more efficient leds out there you can have a fairly bright light running on Two Alkalines with good regulated runtime, and you can store the light for quite awhile with little or no self discharge. Just keep storage area fairly cool. Most emergency lights should be primary AA compatable.

Bill

 

[Fallingwater]

Umm... that's why they have an expiration date. They discharge to 80% at 7 years when stored at room temperature. Check the "Projected Service Maintenance" charts.

Which qualifies as "no significant self-discharge".

30%/month really isn't too bad, thanks for the advice.

Keep in mind that NiMH self-discharge varies widely between brands, and not always in the obvious way.
I've had Energizer NiMHs dead after a few weeks, and eBay offbrand cheapies still holding a charge after two months. Your mileage may vary.

If you want NiMH and care about self-discharge, get some LSD cells such as Sanyo Eneloops (or their many clones).