NiMH Batteries

[gmclam]

All similar batteries not created equal

So, basically what you are saying is to make sure all the batteries are the same brand with the rated MAH, or it will cause problems.

I'd totally diagree with that conclusion. Brand means NOTHING. I've discovered the worse batteries I have are those with big names on them (DuraCell, Energizer, to name 2).

Even batteries from the same package may not age the same. One concept behind functions on chargers like the Maha C9000 is the ability to "analyze" batteries so you can put those together which demonstrate similar values. I've had some "good" 2000mah batteries that rated as good as, or better than, some of those name brand 2500mah+ batteries.

You'll also find that these ratings change depending on charge & discharge rate. The ratings supplied WITH the batteries when you purchase them only provide a single value. So that 2500mah battery may provide that life in a 50ma flashlight, but does not even come close when used in a radio @ 300ma(+) load.

Without any other way to determine which batteries are matched, I guess you have no other choice but to go by (brand &) capacity ratings. However it appears that a much better way to go is to use these fancy chargers and match them based on testing results.

 

[enine]

My experience with those rechargeable batteries in scanners is that they aren't very good. The main problem I have had is that alkaline batteries are normally rated at 1.5 volts and the NiMH batteries are rated at 1.2 volts. My scanner requires 6 batteries, for a total of 9 volts. When I use the MiMH batteries, I hit the ground with less voltage than the scanner requires for operation, so there isn't any room for the voltage drop that is normal with using any batteries. I found that I was constantly recharging batteries that really weren't discharged in the first place. They just didn't have enough voltage in them to run the scanner anymore because they started off being .3 volts lower than what an alkaline battery would be. I went to Radio Shack and bought a 9 volt power supply for $20 and haven't had a problem since. My suggestion would be to save your money and get one of these. Otherwise, you are going to spend a lot of money on NiMH batteries. Of course, none of this matters if you always use your scanner away from home all the time.

The NiMH batteries work much better in my handheld ham radio because it's designed to operate on 7.2 volts.

Alkaline's 1.5v is a no load voltage. Alkaline and NiMH have different internal resistance and different discharge curves. A hot off the charger NiMH is 1.4v and a brand new alkaline is closer to 1.6. However within the first few minutes of use the NiMH will drop down to its 1.2 and the alkaline will go down to 1.3 or 1.4, then after more use the alkaline gradually drops off while the nimh stays flat. For example say you measure each after 2 hours, the nimh will be 1.2 and the alkaline will be 1.3, then two more hours the nimh will be 1.99 and the alkaine 1.2, then two more hours the nimh will be 1.98 and the alkaline 1.1. Then two more hours you'll be at 1.87 and 1.0, etc. etc. So after the initial few minutes they are pretty much the same.

 

[CCHLLM]

I agree, brand means nothing. How well the ones you have on hand match up in your particular setup is what counts. You may have cheapies that match your "expensive" brands perfectly in voltage/charge/discharge performance. Simple volt meter checks as follows will tell you what the virtual performance characteristics of an individual cell, and that's the only way you can judge what "level" it will match up with. Be sure to record the data in a spreadsheet or whatever because you won't remember all the numbers you'll need to know. Mark each cell and follow this sequence:
1) Just before each cell is put into the charger, check the voltage and record it.
2) At the end of charge cycle, check the cell voltage, then
3) let the cell "rest" for 1 hour and test again. These last two figures will give you an indication of the cell's internal discharge rate as it cools and is an indicator of its internal resistance.
4) Just before putting the cell into a discharge cycle, check the voltage. If there's been a period of rest like a day or so, this step, when compared to the reading in step 3, will also indicate the internal discharge rate and tell you which cells are not holding a charge.
5) At the end of the discharge cycle, check the voltage of each cell, then
6) wait an hour and check the voltage again. That 1 hour period will help confirm which cells are dragging the others down because the voltage on a good cell will actually rise a bit.

You'll have to do this through at least three charge/discharge cycles to get a real trending in the data. Once you have all your data, match the cells up into "sets" and mark the sets according to OBSERVED performance, and you'll get the maximum life out of each "set." Naturally some sets will be better than others, but the matching process will extend the performance life of all. If you're not willing to do all this, which doesn't really inhibit your scanning much, well, then I guess you'll just have to continue needless *****in' about supposedly lousy batteries. The process will tell you which ones really are lousy.

 

[rgchristy]

I just purchased a Maha C9000 and 12 Powerex 2700's. I've completed the break-in on 2 sets and am working on the 3rd. Once the sets are used, what should I use as the charging rate for normal charging. DonS's message said between .5C to 1.0C (1350 mA to 2700 mA), but that's a pretty broad range. Patch42's message said 500 mA, and the charger defaults to 1000 mA. I've tried doing searches on here and Google, but can't seemed to find anything. Any help would be appreciated. If it matters, these are for a GRE PSR-500.
Thanks,
Rich

 

[Patch42]

In general, I think slower charge rate is better -- less heat, better battery life -- as long as the rate is not so slow that the charger can't detect the voltage swing that indicates the battery is full. I've been using 500mA with good success on the new Ansmann batteries I bought. They're rated 2850mAh and have been taking mostly in excess of 2900mAh to fully charge. I figure that's a good sign that they're giving me what I paid for.

I've used 1000mA as well without any problem.

If you're in a hurry, jack it up to 1.0C or whatever the charger will provide. If you're not in a hurry, slow it down and let the batteries charge without getting hot. If they're still charging after you know they should be full, then I'd use a higher charge rate next time.

 

[Grog]

I'd agree with Patch42

 

[rgchristy]

Since I have 3 sets in rotation plus 2 extra older sets as spares, I'm in no hurry. I'd rather not cook them. I think I'm going to start with the 500 mA and see how that goes. Thanks for your input.
Rich

 

[Zaratsu]

I've had good luck with the Sanyo HR-3U 2700 Ni-MH.

They last MUCH longer than my eneloops, which I have not been thrilled with after all the hype.

I got them when I bought the scanner and charge them in the scanner, while the eneloops usually go into a radioshack 6 hour charger. I discharge all the bats in an old handheld Sony TV that really sucks them down to nothing.

These sanyos have Superlattice Alloy Evo written on them, whatever that means. Dont know if it matters, but I like them. Getting around 12 hours on the scanner with the speaker turned up to medium and the light used fairly frequently.

 

[screenersam]

I have two Pro-97s (carry one to work); every night I plug in the work one, charge it overnight, and charge the other thru the day. been doing this for about a year; no problem. using some cheapo 2000 mha ("Digital" brand name?). I've used Energizer 2700s for other uses; no probs so far.

 

[SCPD]

My experience and opinion is that cheaper batteries and chargers cost more in the long run. I've been using PowerEx batteries and Maha chargers for 9 years now and I'm still using some of the first PowerEx batteries I purchased in 1999. I've had about 60 of these batteries and only one has gone bad.

As for charging rates, it is important that the rate is not higher than 10% of the capacity. I've seen that stated on several websites. So for a 2700 mAh battery a charge rate of less than 270 mA is recommended. That slow of a rate may not be available in some of the lower cost chargers. My 2700's take about 12-14 hours to charge and the reconditioning function on my Maha charger requires the battery be in the charger for about 36 hours. I never use the higher charging rate available in my charger.

Because I use the latest Maha chargers, I've been able to have batteries last 9 years now and in the long run the more expensive charger has saved me in replacement cost. I use my batteries for flashlights, office equipment, the wireless mouse and keyboard for my desktop computer, digital cameras, and three handheld scanners.

 

[enine]

Same here with the maha's. Now I will contradict Exsmokey on the 10% rule, according to the maha manual and the battery experts at cpf too slow of a charge makes the termination easier to miss and less consistent. I'm having the best results with 1c for eneloops which is perfect because the wife can just pop hers in and hit enter a couple times as thats the default on the c9000.

DanTSX you don't want to discharge NiMH down to nothing, they can get into a polarity reversal state, plus you don't need to discharge them anyway. A full discharge every 20 times or so is the current recommendation. Get a charger like the c9000 or the lacross which will do the discharge cycles to the correct minimum voltage.

Brand can make a difference over the long term, I have Sanyo's dating back to 1999 that still have 80% capacity while I have Rayovac's that are bought in 2004/5 that are at 80% capacity. The sanyo's have lasted twice as long now with the same wear.