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How long is a Ni-MH supposed to last?

post #1 of 15
9/27/01 at 6:26pm
Thread Starter 
The battery that came with my Portable Minidisc won't charge anymore. I've had it for little over a year now and recharged it about once every 2 weeks on average. I used to get about 5 hours out of it, now only half an hour. Is it normal these batteries have such a short life?
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post #2 of 15
9/27/01 at 6:56pm
battery life does get less over time. I believe nihm's also age faster than nicd's.

it sounds like you've blown them tho. overcharging kills nihm batteries. I had a nihm that didn't reach the end of an md at one point, got a pair of new ones then.

just get some 1600mAh batteries, they're not so expensive.
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post #3 of 15
9/28/01 at 11:57am
I'm using a Sony BP-DM20 1200mah NimH in my discman and i've had it about 3.5 years and it's been used constantly. I just noticed yesterday that theres some kind of rust starting to come out around the contacts on the end but they still get about half of their original cycle (about 4 hours instead of 8). This has been deteriorating very very slowly for a very long time. I charge them when they're dead or almost dead and they don't overcharge, my discman says Charge on the display until they're done and then it stops. I'm just about to put my GP 1500mah's into service for longer battery life. I couldn't find any 1600's.
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post #4 of 15
10/7/01 at 9:01pm
NiMh last longer then the NiCd. You can charge them from any where of 500 to 1000 times till they lose there charge faster. I have to replace my MD battery which is a lithium which will run me 50 to 70 dollars. : ( i gues thats what you pay for a hi end MD with a special battery.

Garrett
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post #5 of 15
10/7/01 at 9:27pm
NiMH cells have a higher energy density than NiCds but typically only 2/3 to 1/2 the useful charge/discharge lifespan. They are also more sensitive to overcharging than NiCds. Contrary to popular opinion, NiMH batteries are not completely immune from memory effect. Heat is the real killer of NiMH cells. For max lifespan your charge rate should not exceed 1/10 of the cell's capacity. i.e. if you have a 1600mAH cell, don't let the recharge current exceed 160mA. The same actually holds true for discharge rates as well, since this will directly affect the cell's internal temperature. So, you see, depending upon the application, NiCd may be a better solution than NiMH. Things are improving all the time however!!
Cheers!
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post #6 of 15
10/13/01 at 10:33am
I agree with Kwkarth. I have used Ni-Mh cells in My Discman for 5 years (The 1200MAh Radio shack AA) and thay still get 3/4 of the run time thay did when new and this would not have been noticed if i did not note the run time when new on the Cell. I also use AAA's in my Headphone Amp's and i have over a year on some of them and still get the same runtime as when new. I measure runtime by conecting a Current source to draw a specified Current from them and note any changes. One thing that suprised me was when in one of My amps the Series pass transistor charging the battery from a max712 shorted and thus put the full 1.5 amps from the Powersupply into the battery Pack of 16 AAA Cells. I went to pick up the amp and got burned Ouch way hot. This was from the batteries Heat. Not only was i shocked to see the amp still worked But still got my normal Playing time out of them. Since the heat caused the Plastic Wrap on the Cells to swrink I got batteries Plus to make me a new pack for saftey reasons. i now also fuse the Power supply. Now 9 volt NI-Mh I have a problem With That is why do not use them in any amps anymore just Meters and other stuff. Oh yes the Charge and discharge rates that Kwkarth recomends is a good choice.
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post #7 of 15
10/13/01 at 9:16pm
btw mine used to last about 8 hours and I charged them every 2 days. Now they last about 4 hours. And that is with a Sony discman that has a really high charge rate that only takes about 3 hours. This is why I can't use my new GP batteries until I get a charger that won't charge them too fast, like my discman would.
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post #8 of 15
10/14/01 at 11:25am
This debate between NiCd vs. NiMH rechargeables sucks...

I have had NiCD batteries becoming unusable after only a few uses (even though I used a slow overnight charger on them). Maybe it's the faulty cells... What a pile of crap! Worse, NiCD batteries are becoming extremely difficult to find in retail stores across the U.S.! (Except maybe RadioShack.) Even when new, I found AA NiCD rechargeables (other than the RS 1000mAh ones) deliver only about 4 to 5 hours of playback between charges on a Sony CD Walkman that's rated to run 38 hours of playback on two AA alkaline batteries.

As for kwkarth's advice not to allow the discharge rate rise above 1/10 of the current capacity of a given NiMH battery, it isn't possible with most portable audio devices that uses mechanical motors! You see, those devices have a peak current draw that exceeds that amount - even if your NiMH's are rated at 1800mAh!
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post #9 of 15
10/14/01 at 1:21pm
I think He means Continious current as a temp spike or surge is not going to be long enough to be heating the batteries. as for Nicads Thay are going away because of the use of caddium. a heavy metal. I get 12 Hours of play time on my Panasonic SL-SW860 with The radio shack 1200 MAh NI-Mh. and that is fine for me. Also i think All Portable Audio gear from radios to headphone amps sound Better on Both Ni-cad's and NI-MH than on Alkiline types. Just My 2c Worth...
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post #10 of 15
10/14/01 at 2:14pm
Quote:
Originally posted by ppl
I think He means Continious current as a temp spike or surge is not going to be long enough to be heating the batteries. as for Nicads Thay are going away because of the use of caddium. a heavy metal. I get 12 Hours of play time on my Panasonic SL-SW860 with The radio shack 1200 MAh NI-Mh. and that is fine for me. Also i think All Portable Audio gear from radios to headphone amps sound Better on Both Ni-cad's and NI-MH than on Alkiline types. Just My 2c Worth...
You are correct about continuous current drain. It's just a rule of thumb anyway. The "fast" charge batteries are designed to survive higher currents, but in my experience, their lifespan is diminished in spite of what the ad copy on the side of the package says.

As far as NiCD and NiMH batts sounding better than alkalines or carbonZincs... I have to agree with the reasoning since the internal resistance of the rechargables is WAY lower than that of the non-rechargables. This means that without any other regulation, an alkaline supply won't be near as "stiff" as a NiCd or NiMH one. When your music or equipment demands a huge transient, the NiCd supply will hold up, but the alkaline supply will sag at that instant because it cannot supply as much instantaneous current due to internal IR (current x resistance) voltage drop.
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post #11 of 15
10/14/01 at 3:11pm
NiMH still suffers from memory effect, as kwkarth said, though MANY companies are claiming otherwise. For example, sony claims that their NimH don't suffer from memory effect, but if your read their fine print, that's not really the case.

Also, IMO, Sony charges their "gumstick" batteries way too fast, 4 hours for a complete charge, and 1500mAh capacity. The batteries really get quite warm, and i'm sure it reduces their lifespan drastically.... but it does force you to replace them more often, allowing them scam another $100/pair off you...
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post #12 of 15
10/14/01 at 3:31pm
Quote:
Originally posted by thomas

Also, IMO, Sony charges their "gumstick" batteries way too fast, 4 hours for a complete charge, and 1500mAh capacity. The batteries really get quite warm, and i'm sure it reduces their lifespan drastically.... but it does force you to replace them more often, allowing them scam another $100/pair off you...
Bingo!!
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post #13 of 15
10/15/01 at 1:54am
Quote:
Originally posted by kwkarth


Bingo!!
That's right; quick-charging of any type of rechargeable battery significantly shortens the usable life of the cell. The 1000-recharge-cycle claim assumes that you'll be charging at 1/10 of the cell's rated capacity for about 10-12 hours. The truth is most rapid- or quick-chargers charge at a MUCH higher rate than that. The end result is that with modern rapid chargers that charge batteries completely fully (regular or "overnight" chargers NEVER even come close to fully charging the NiCd or NiMH batteries, IMHO, due to the memory effect building up over the long recharging time), the usable lifespan of NiCd or NiMH rechargeable batteries has been reduced to about 300 charge/discharge cycles (instead of 1000). Hope this helps.
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post #14 of 15
10/15/01 at 2:20am
Quote:
Originally posted by Eagle_Driver


That's right; quick-charging of any type of rechargeable battery significantly shortens the usable life of the cell. The 1000-recharge-cycle claim assumes that you'll be charging at 1/10 of the cell's rated capacity for about 10-12 hours. The truth is most rapid- or quick-chargers charge at a MUCH higher rate than that. The end result is that with modern rapid chargers that charge batteries completely fully (regular or "overnight" chargers NEVER even come close to fully charging the NiCd or NiMH batteries, IMHO), the usable lifespan of NiCd or NiMH rechargeable batteries has been reduced to about 300 charge/discharge cycles (instead of 1000). Hope this helps.
Interesting thing is that even at 1/10 capacity charge rate NiMHs are only rated for about 600 cycles as opposed to NiCds 1000. Oh well, that's progress! At least the energy density is higher in NiMHs and they're not as toxic as NiCds.
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post #15 of 15
10/15/01 at 2:21pm
As I said, despite the 4 hour charge my Sony NiMh battery still lasts for almost 3/4 of what it did when it was new almost 4 years ago now. This is longer than the average person has a discman.
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