That really depends, I personally can't remember any device in my house that can take alkaline batteries, but not rechargeable batteries. Maybe HKJ can give you some examples?
I have one of those cheap fibre optic desk lamps with all the strands that won't run on eneloops. They take 3 x AAA and have no problems with alkalines. What is confusing is that they will run down the alkalines after hours and hours of continuous use, yet won't even turn on with fully charged eneloops.
What I can say is that on my Nitecore EA81 that takes 8 x AAA, the eneloops are just incredible. With alkalines, you just use turbo briefly a couple of times and then the flashlight will only go to high thereafter. With the eneloops, turbo seems to last amazingly long, maybe 5 or 10 times longer or more than the alkalines. I'm really not sure why they are that good in this particular flashlight, but they are. They may last even longer in turbo than what I am saying as I have not charged them for a long time and it is still working.
The voltage of the NiMh (1.2 V) cells is lower than the alkaline (1.5 V). Some devices will not accept the lower voltage. Try them and see what happens with a particular device. And, of course, the discharge patterns are different.
@chibiM, on my Nitecore EA81 that is running 8 x AA eneloops, after charging and using the light for a short while, I tested the battery voltage and they range from 1.424v to 1.415v. Is that within the safe limits to run all eight batteries in one light?
Ideally, what you’d want to do is buy an analyzing charger that allows you to do a discharge test, or something like a ‘break-in’ function (as found on the Maha C9000) and match your closest 8 Eneloops, since that’s a lot of batteries to run in any device, let alone a high current flashlight.
I have the MC3000 but never used it yet for my eneloops. I have to get going on it to see if I can get a closer match. I gave another EA81 to my brother and when I tested just the voltage on those eight batteries that were inside it, the voltage was exactly the same for all of them.
klrman, I think that is fine! Not sure how much of a difference they were beforE they were used in the light, but just to be on the safe side, I would not let the light run out of batteries. Because that would cause the weakest of the bunch be much deeper discharged than the rest.. and the second round that weak battery will become even weaker, and the third round even weaker.
So better charge them when they arent empty yet. You might see a difference in output when they get empty, and that might be a good time to recharge them.
The interview question and answers for the Eneloop technicians are on the website. Until I have time to put them 1 by 1 in the correct section on the website, they can be found here: https://eneloop101.com/interview-with-eneloop-technicians/