nmh Battery drain

[GeoBobC]

I purchased four 2650 mAh Duracell rechargeable batteries recently. I noticed that my GPS was going dead after only a few hours use, spread over several days. I got suspicious. With a full charge, the batteries ran 8 hours and the GPS still displayed a full charge. Next, I fully charged the batteries and checked the voltage. When I first took them off the charger they read 1.37 volts. Two hours later they read 1.34. Another two hours they read 1.30 volts.

 

I now suspect that the batteries are draining very quickly while not in use. After a week of this rapid draining, it's likely they would only go a few hours in the GPS.

 

Does this sound normal? I've read that batteries discharge when not in use, but I lost over 5% of the charge in just a few hours.

[beautyisgod]

I purchased four 2650 mAh Duracell rechargeable batteries recently. I noticed that my GPS was going dead after only a few hours use, spread over several days. I got suspicious. With a full charge, the batteries ran 8 hours and the GPS still displayed a full charge. Next, I fully charged the batteries and checked the voltage. When I first took them off the charger they read 1.37 volts. Two hours later they read 1.34. Another two hours they read 1.30 volts.

 

I now suspect that the batteries are draining very quickly while not in use. After a week of this rapid draining, it's likely they would only go a few hours in the GPS.

 

Does this sound normal? I've read that batteries discharge when not in use, but I lost over 5% of the charge in just a few hours.

 

is your backlight at maximum the whole time? i only use 50% and only when it is needed...i am not sure if this really make a difference...but in the option you can change the "battery type" from alkaline to Ni-MH or Lithium...but i think that only helps you with the charge level accuracy only...and what model is your gps? is it 60CSX?

[+Red90]

What model GPSr? Do you have the battery indicator set for NiMH? The voltage sounds fine.

 

These are discharge curves for NiMH cells.

[GeoBobC]

My problem is that the batteries are draining with the unit off, so backlight isn't a factor.

[GeoBobC]

Red90: your chart suggests that voltage does drop more rapidly after charging. What would be helpful is to know over what period of time that drop occurs. I've read two versions: one that suggests the voltage drop is 1%/day, and another that suggested the drop could be 10% the first day. Quite a difference. I suspect my batteries and chargers are fine, but my expectations may not be. Leaving nmih batteries in the GPS for an extended period of time will definitely result in a loss of charge. The 18 hours quoted for battery life in a 60cx assumes no loss of battery capability. That would be true for alkalines, but not for rechargeables since they're losing capacity even when the unit is off, sitting on the shelf. Maybe 10-12 hours is more reasonable if the batteries are in the GPS for a couple weeks.

[Tahawas]

GeoBobC, I think your charger isn't designed for these high capacity batteries. I just received 12 2700 mAh Powerex batteries, 2 days ago. The four charged that day are now all at 1.60 V. The four charged yesterday area all at 1.65 V. The four charged about 8 hours ago are all at 1.70 V. None have been installed in anything.

 

These voltages are higher than I've ever seen for NiMH batteries, but I've never had anything over 2300 mAh. My guess is that these batteries get some of their extra capacity by using a different chemistry, and your charger uses voltage to limit overcharge, so it isn't really charging them.

 

These voltages are NOT wrong, though I did round them to 3 figures. I use a Beckman Tech 310 multimeter, intended to be usable for calibrating other meters.

[+Red90]

The batteries should settle to around 1.2 Volts and still be fully charged.

 

Again what unit? If it is a 60Cx, you should be getting 18 to 20 hours from new 2500 mA-h NiMH. I have ones and have kept track off uage times.

[+Prime Suspect]

If these are brand new batteries, remember that you're not actually getting a full charge yet. It takes about 10 discharge/recharge cycles before NiMHs will charge to their full capacity.

[+BigLarry]

My NiMH rechargeable AA batteries all have around 1.31-1.35 V fully charged, and drop to around 1.2 when drained.

Right after taking off the charger, they have a higher voltage, but it quickly settles down to the above value over an hour or two, even while sitting on the counter. That's normal. The charger needs to drive at a higher voltage to pump in current, and it takes a while for the battery to settle down after matching this excess charge voltage.

 

My 2700 mAh batteries from PowerEx last ~25 hours in my 60CSx.

[Donald, Daisy and Kids]

I purchased four 2650 mAh Duracell rechargeable batteries recently. I noticed that my GPS was going dead after only a few hours use, spread over several days. I got suspicious. With a full charge, the batteries ran 8 hours and the GPS still displayed a full charge. Next, I fully charged the batteries and checked the voltage. When I first took them off the charger they read 1.37 volts. Two hours later they read 1.34. Another two hours they read 1.30 volts.

 

I now suspect that the batteries are draining very quickly while not in use. After a week of this rapid draining, it's likely they would only go a few hours in the GPS.

 

Does this sound normal? I've read that batteries discharge when not in use, but I lost over 5% of the charge in just a few hours.

 

In my experience, ALL rechargeables will take a few sycles to accept full charge.

 

I have experienced upto 15 full cycles before full charge is accepted on new NIMH's.

 

I have 20 AA's primarily for my Garmin Vista CX but also for other toys, games etc and after the few cycles and they are accepting full charge, I charge them up and leave them. Sometimes they sit for 4-5 weeks with no noticable discharge.

 

I use a Duracell 1hr fastcharger and 2500mah energizers as well as 2600Mah polarpower's and have not had a problem since!

[WR8Y]

I've read that batteries discharge when not in use, but I lost over 5% of the charge in just a few hours.

There are a LOT of good posts in this thread, but I wanted to add two things:

 

1) A 5% drop in terminal voltage is NOT an indication of a 5% drop in current source capacity. Battery voltage isn't always a good indication of chage. My cheap Dollar General batteries loose terminal voltage on a very erratic scale, and will go from 3.0 volts (for two batteries) to 2.6 in about an hour. Then they sit at 2.5 or 2.6 volts for 4 or 5 hours! And NiMah batteries are even weirder!

 

2) Aw, hell. I forgot my next point!

 

In any event - make sure you read the three posts before this one!!

Edited September 29, 2006 by WR8Y

[GeoBobC]

Thanks for all the feedback. I am tentatively concluding that (a) my batteries are probably close to normal; ( I should be getting at least 16 hours on a full charge; © batteries do lose their charge over time, so the longer it has been since they were charged, the less capacity they have.

 

If I take the conservative self-discharge rate of 1%/day (some state up to 5%/day), then after 30 days the batteries have lost 30% of their charge. Assuming they would run a 60cx 18 hours at full charge, I interpret that to mean they would run a 60cx only 12-13 hours (70% of 18) after one month. That's probably close to what I'm experiencing.

[Photobuff]

I'm sure it's been in a hundred other posts on batteries, but go to batteryuniversity.com and absorb everything they have to say, remembering that NiMh and Li technologies are still changing pretty rapidly. Agree that several charge cycles are necessary to develop full capacity. Also, rapid charging may not get you all the way there- some amount of trickle charging is necessary, though in general NiMH cells should not be trickle charged for long periods of time. The self discharge rate of NiMh batteries is significant, so I always charge right before use if I know I'll need all the energy.

[+sock-it-2-me]

THis is a problem with NiMH bats. I use them in radio control airplanes. They recommend they be charged right before use. I tried using a set one month after charging them and they had very little juice left in them.

 

However, your case seems to be a bit extreme.

[beautyisgod]

I purchased four 2650 mAh Duracell rechargeable batteries recently. I noticed that my GPS was going dead after only a few hours use, spread over several days. I got suspicious. With a full charge, the batteries ran 8 hours and the GPS still displayed a full charge. Next, I fully charged the batteries and checked the voltage. When I first took them off the charger they read 1.37 volts. Two hours later they read 1.34. Another two hours they read 1.30 volts.

 

I now suspect that the batteries are draining very quickly while not in use. After a week of this rapid draining, it's likely they would only go a few hours in the GPS.

 

Does this sound normal? I've read that batteries discharge when not in use, but I lost over 5% of the charge in just a few hours.

 

In my experience, ALL rechargeables will take a few sycles to accept full charge.

 

I have experienced upto 15 full cycles before full charge is accepted on new NIMH's.

 

I have 20 AA's primarily for my Garmin Vista CX but also for other toys, games etc and after the few cycles and they are accepting full charge, I charge them up and leave them. Sometimes they sit for 4-5 weeks with no noticable discharge.

 

I use a Duracell 1hr fastcharger and 2500mah energizers as well as 2600Mah polarpower's and have not had a problem since!

 

it was interesting to know that it takes a few (10) rechargeables cycles to accept full charge...i didnt know that...really interesting...why is that? why a few cycles?

[Inukshuk94]

I'm going to jump in here in another note. Are there any battery chargers for Lithium AA?

[itchytweed]

If you have a DMM, just turn the GPSr off and route the battery path through the ammeter terminals and see if you are getting current flow. You may see a hair of flow to operate the on/off switch circuit. Then compare that flow to what you read when the unit is on.

 

Also, fast charging may bring the terminal voltage up to a useful level but the battery has not had time to absorb the charge. The chemistry can only convert so fast. I prefer normal desk chargers and keep several Ni-MH sets available - one in, one out and two in the charger on trickle. The sets are always rotated to keep them charged.

 

Good Luck.

[GeoBobC]

To add to the mystery: I took some older 2500 mah niMH batteries and charged them in the same charger. When the charger stopped charging the batteries read 1.46 volts on a voltmeter, vs. 1.37 at full charge for the newer 2650 mah batteries in question. The older 2500 mah batteries last much longer in my GPS.

 

Are the 2650 batteries defective, or have they not been through enough cycles? I've charged them at least six or seven times.

[+Prime Suspect]

I'm going to jump in here in another note. Are there any battery chargers for Lithium AA?

There are about a dozen different types of Lithium batteries, each with their own chemistry. Some are rechargeable, but many aren't. If it's not labeled as a rechargeable, it probably isn't.

[+JRMoney]

I'm new at the rechargeable thing. What type of NiMH batteries and charger would you suggest?

[beautyisgod]

I'm new at the rechargeable thing. What type of NiMH batteries and charger would you suggest?

 

2700mAh NiMH Rechargeable AA Batteries 4pc Pack w/ Carrying Case.

[Vibramhead]

I'm new at the rechargeable thing. What type of NiMH batteries and charger would you suggest?

 

You might want to look specifically at the new Sanyo 2700 MAh, model HR-3U. They use some kind of proprietary chemistry that is supposed to substantially reduce drain while inactive. I've been using them in my 60csx for a couple of months, and consistently get 18-20 hours per charge, even when I haven't charged them recently. I got mine from Thomas Distributing: http://www.thomas-distributing.com/index.htm.