What's the Best Battery Charger?

[Kevin Rooney]

Kevin- I suggest you get a totally dead cell and convince yourself that charging will start after enough charge has entered the battery so that the charger can see "something".

Thanks - I have a couple of batteries in my stash of AA's and AAA's which I suspected were toast, perhaps damaged by the "dumb" charger I'd been using. The cases appear to have swelled, causing the wrap to separate slightly. When I put one of them in the charger, it repeatedly displayed "Null", so that tells me battery is of dubious value anyway. Helps me justify the purchase of the Sanyo Eneloops

 

[DougPaul]

My Maha chargers will start charging a totally flat battery within 30 minutes. I have put a dead cell in and nothing happened immediately. After some time, the charge light came on.

I haven't observed this--occasionally I have looked at the charger after several hours and seen the red light still flashing... But it may depend on the cell and specific charger. I'll watch for it (but I rarely try to charge a really dead/flat cell*). The trickle charger always managed to put some charge in some really worn/damaged cells when the smart chargers refused to do anything with them.

Thanks - I have a couple of batteries in my stash of AA's and AAA's which I suspected were toast, perhaps damaged by the "dumb" charger I'd been using. The cases appear to have swelled, causing the wrap to separate slightly. When I put one of them in the charger, it repeatedly displayed "Null", so that tells me battery is of dubious value anyway. Helps me justify the purchase of the Sanyo Eneloops

If they have swollen or leaked, discard them. The electrolyte is pretty corrosive and may damage whatever you put them in.

Someday the Eneloops will be old and tired too... (NiMHs are typically rated for ~500 (full) cycles.) And you will probably replace them with no regard for their feelings...


* Running a cell down to zero V (totally flat) or reversing it while trying to get the last bit out of a group of cells can damage it. It is much better for the cell to stop when its voltage drops down to 1 V. You have used almost all of the energy in the cell by this point anyway. (My GPS, for instance, uses 2 AA cells and shuts down at 2V, thus protecting the cells from damage. LED lights should also generally be safe for NiMHs, but incandescent lights would not be safe.)

Doug

 

[LivesToHike]

Thanks

I've also had alot of trouble with a quick charger, and even my "supposed" slow charger also cooking my NiMd batteries; I use the same Energizer AA batteries mentioned by folks. My batteries now rarely hold a charge for more than a few days - I've been caught by this during summer hikes - my camera's lense deployed and then went into a very deep, deep sleep.

I'm going to put one of the Maha slow chargers mentioned on my wish list for the end of the month or early next month.

Thanks everyone for sharing your experiences and recommendations.

Best,
--Mike

 

[DougPaul]

I've also had alot of trouble with a quick charger, and even my "supposed" slow charger also cooking my NiMd batteries; I use the same Energizer AA batteries mentioned by folks. My batteries now rarely hold a charge for more than a few days - I've been caught by this during summer hikes - my camera's lense deployed and then went into a very deep, deep sleep.

I'm going to put one of the Maha slow chargers mentioned on my wish list for the end of the month or early next month.

Two to four hour smart chargers are generally safe for NiMH cells. (See, for instance, my recommendations earlier in the thread.) If the cells become too hot to touch for any length of time, they are too hot and are likely to become damaged. (Overheating while charging is a common way of damaging the cells.) One of my chargers has a temp sensor and sometimes suspends charging during a 2-hr charge to let the cells cool down. (The sensor is external to the cell and may be set conservatively. Another charger with a similar charge rate has never shown any cell damage.) I use a fan to put a gentle cooling breeze on the cells and it fixes the problem. In general, putting a fan on the charger and cells isn't a bad idea..

Some chargers are notorious for overheating the cells: eg the Ray-o-Vac PS-4 which had a 1 hr charge rate (with the switch set to NiMH). If you set the switch to NiCad, it had a 2 hr charge rate which was safe for NiNH cells.


Once overcooked, the cells are permanently damaged--the only thing you can do is replace the cells and the charger.

Doug

 

[LivesToHike]

Hmmm, point taken.

Two to four hour smart chargers are generally safe for NiMH cells. (See, for instance, my recommendations earlier in the thread.) If the cells become too hot to touch for any length of time, they are too hot and are likely to become damaged. (Overheating while charging is a common way of damaging the cells.) One of my chargers has a temp sensor and sometimes suspends charging during a 2-hr charge to let the cells cool down. (The sensor is external to the cell and may be set conservatively. Another charger with a similar charge rate has never shown any cell damage.) I use a fan to put a gentle cooling breeze on the cells and it fixes the problem. In general, putting a fan on the charger and cells isn't a bad idea..

Some chargers are notorious for overheating the cells: eg the Ray-o-Vac PS-4 which had a 1 hr charge rate (with the switch set to NiMH). If you set the switch to NiCad, it had a 2 hr charge rate which was safe for NiNH cells.


Once overcooked, the cells are permanently damaged--the only thing you can do is replace the cells and the charger.

Doug

Thanks, Doug. I have a Ray-Vac charger and a Durcell chargers, but I'll have to verify the model #'s. I think the former takes more than a 60 minutes (4+ hours), and the latter takes anywhere from 15 to 60minutes to charge 4 AA NiMd's.

Regardless, both these chargers appeared to have overheated cells. The cells are still very warm when the charger has finished, giving me the impression that the charger hasn't really shutdown charging, or that the trickle charge really isn't a trickle. I've never measured the current draw, but that would be easy to do if I wanted to know.

I'll just replace all my AA cells and the charger as you suggested.

--Mike

 

[DougPaul]

Regardless, both these chargers appeared to have overheated cells. The cells are still very warm when the charger has finished, giving me the impression that the charger hasn't really shutdown charging, or that the trickle charge really isn't a trickle. I've never measured the current draw, but that would be easy to do if I wanted to know.

In general, the cells get quite warm in the last bit of charging.

In the early part of charging, most of the charging energy is absorbed in chemical changes in the cell (ie the charging). Once the chemical changes have completed (ie the cell is fully charged), most of the charging energy goes into heating the cell. The resulting increase in temp can be used to terminate charging if the charger has a temp sensor. It also causes the voltage across the cell to drop slightly which is also used as a cue to terminate charging. (Most smart chargers switch to a slow trickle rate (typ <= ~50mA) rather than completely stop charging.)

So a certain amount of heating is normal, but too much is not.

The above is why you want a smart charger--it knows when to stop charging. If it does not stop the cell will ultimately overheat. (This is why timer-based chargers are bad--the user has no way of knowing the proper charging time and eventually the cells will be damaged by overcharging and overheating after the user has overestimated the time.)

BTW, charging too slow is also not the best for NiMH cells--the reactants develop a poor crystal structure and do not work as well as they should. A charging rate of ~.2C to ~.5C is best, but it must be stopped before the cell becomes overcharged.


The MH-C401fs charger has a switch for fast (1000mA ~ .5C ~ 2hr) or slow (300mA ~.2C ~ 5hr) charge rates--a nice feature, IMO. I normally use slow to be more gentle to the cells unless I am in a hurry. (I've seen no evidence that the fast setting has damaged any of my cells.) A number of other chargers also have selectable charging rates.

If you have the Ray-o-Vac PS-4 charger, just use it on the NiCad setting for NiMH cells (900mA ~ 2hr rate) and it should be fine. (The NiMH setting is a 1800mA ~ 1hr rate.)

BTW, for typical NiMH AA cells (2000mAh--2700mAh):
2hr rate ~ .5C ~ 1000mA
4hr rate ~ .25C ~ 500mA
trickle <= ~.02C ~ 50mA

A nice reference on charging NiMH and NiCad batteries is http://www.batteryuniversity.com/partone-11.htm

Doug

 

[LivesToHike]

In general, the cells get quite warm in the last bit of charging.

In the early part of charging, most of the charging energy is absorbed in chemical changes in the cell (ie the charging). Once the chemical changes have completed (ie the cell is fully charged), most of the charging energy goes into heating the cell. The resulting increase in temp can be used to terminate charging if the charger has a temp sensor. It also causes the voltage across the cell to drop slightly which is also used as a cue to terminate charging. (Most smart chargers switch to a slow trickle rate (typ <= ~50mA) rather than completely stop charging.)

So a certain amount of heating is normal, but too much is not.

The above is why you want a smart charger--it knows when to stop charging. If it does not stop the cell will ultimately overheat. (This is why timer-based chargers are bad--the user has no way of knowing the proper charging time and eventually the cells will be damaged by overcharging and overheating after the user has overestimated the time.)

BTW, charging too slow is also not the best for NiMH cells--the reactants develop a poor crystal structure and do not work as well as they should. A charging rate of ~.2C to ~.5C is best, but it must be stopped before the cell becomes overcharged.


The MH-C401fs charger has a switch for fast (1000mA ~ .5C ~ 2hr) or slow (300mA ~.2C ~ 5hr) charge rates--a nice feature, IMO. I normally use slow to be more gentle to the cells unless I am in a hurry. (I've seen no evidence that the fast setting has damaged any of my cells.) A number of other chargers also have selectable charging rates.

If you have the Ray-o-Vac PS-4 charger, just use it on the NiCad setting for NiMH cells (900mA ~ 2hr rate) and it should be fine. (The NiMH setting is a 1800mA ~ 1hr rate.)

BTW, for typical NiMH AA cells (2000mAh--2700mAh):
2hr rate ~ .5C ~ 1000mA
4hr rate ~ .25C ~ 500mA
trickle <= ~.02C ~ 50mA

A nice reference on charging NiMH and NiCad batteries is http://www.batteryuniversity.com/partone-11.htm

Doug

Doug, Thanks for your follow-up message - esp about the short charging for NiMH cells.

I'm fairly certain my Ray-o-Vac is not the PS-4 model, I think what I have instead is a fairly dumbed-down NiCad/NiMH battery charger.

Great reference article! The most telling quote in the article you referenced was: "The battery should cool to room temperature when on trickle charge. If the temperature remains above room temperature after a few hours in ready mode, the charger is performing incorrectly."

I'm fairly certain my batteries are very warm to the touch after they've 'finished' charging and are on trickle charge. I'm convinced that my existing charger is doing the wrong thing.

--Mike

 

[DougPaul]

I'm fairly certain my Ray-o-Vac is not the PS-4 model, I think what I have instead is a fairly dumbed-down NiCad/NiMH battery charger.

My PS-4 says "PS4" on the bottom.

Great reference article! The most telling quote in the article you referenced was: "The battery should cool to room temperature when on trickle charge. If the temperature remains above room temperature after a few hours in ready mode, the charger is performing incorrectly."

I'm fairly certain my batteries are very warm to the touch after they've 'finished' charging and are on trickle charge. I'm convinced that my existing charger is doing the wrong thing.

That sounds like the "trickle" is too high a current or the charger has not detected a full cell and is continuing to supply a full charging current. Either can damage NiMH cells. As noted in one of my earlier posts, a NiCads can take a higher trickle current than NiMH so a possible cause of a high trickle current is mis-auto-cell-type determination or just bad design of the charger.

FWIW, I generally remove the cells from the charger as soon as I notice that the charger is indicating "full charge".

Doug

 

[DougPaul]

I have seen reports that a number of LaCrosse BC-900/BC-9009 chargers have overheated both the charger and the cells including melting some of the plastic, often described as a meltdown. There is some evidence that the problem was fixed in firmware versions v35 and v36. (The version number is visible on the right at turn-on.) As such, I am rescinding my recommendation of the BC-900 charger.

FWIW, I have had no problem with mine so far (v35 firmware). However, I always run a fan on mine when using them because some of the cells used to get a bit hot during charging. I have no idea whether the fan will prevent the problem, should it occur.

For more info, see http://www.candlepowerforums.com/vb/showthread.php?t=253907. This link is a survey and shows reports for a variety of models and firmware versions.

A search brings up lots of reports: http://www.google.com/search?as_q=l...q=BC+900+&as_sitesearch=candlepowerforums.com

I'm still researching the issue.

Doug

 

[psmart]

I have seen reports that a number of LaCrosse BC-900/BC-9009 chargers have overheated both the charger and the cells including melting some of the plastic, often described as a meltdown. There is some evidence that the problem was fixed in firmware versions v35 and v36.
Doug

FWIW, my BC-9009 has been trouble free with v35. There was a power supply recall and replacement due to overvoltage problems - sounds like this could be related to the overheating.

 

[TomK]

Any update on this subject?

Thinking about getting a decent set of rechargable batteries and a charger for them.

Mostly for a Garmin GPSmap 62S - I use it about 6 hours a week. Been using 2500 mAh NiMh AA's charged using a Radio Shack charger that charges either 2 or 4 at a time, feeds each pair 170 mA and turns itself off after 13.5 hours. So, per the instructions, I charge for 4 hours, reset it, and run it the remaining 13.5 hours until it turns itself off to get the 17.5 hours of charging that the instructions tell me these batteries need.

But the batteries are at least 5 years old now, have gone through a fair number of charge/discharge cycles. Today I went through 3 (!) pairs in about 2 hours, which tells me that they aren't holding a charge well anymore, and I really need to replace them. The cold temps today may also have something to do with that.

Thinking I ought to spring for one of those fancy chargers that charge each cell independantly, can charge/discharge, analyse etc. Would rather buy quality and cry once. Prefer a charger that is gentle on the cells, and won't harm them. Don't really need to charge quickly, happy to let the charger take it's time if that is better for the batteries. Don't need to charge more than 4 cells at a time.

The info in this thread is close to 10 years old - any developments folks ought to know about?

Besides a charger recomendation, suggestions for the batteries themselves?

Also, where might I actually go to see/purchase - I'd rather make the purchase in person than over the internet (I'm weird that way). Lowes/Home Depot? Best Buy? Someplace I hadn't thought of? Was thinking of a road trip to U Do It in Needham, but thier web site doesn't seem to show much in this area...

Thanks in advance...

TomK

 

[DougPaul]

The advice in this thread is still basically sound. A smart charger that charges the cells individually at a moderate rate is best for the cells. (Low charging rates may seem to be gentler but are not best for the cells. Too high a charging rate will overheat them.)

FWIW, I have standardized on the lower capacity (2000 mAh for AA, 800 mAh for AAA) Eneloop low-discharge cells. They have a longer lifetime (more cycles) and are more (electrically) rugged than the higher capacity models. I use these cells in both my headlamps and GPSes. (My spares are more of the same and/or lithium non-rechargables.)

My main workhorse charger is still the Maha MH-C401FS. Recently bought another one...


BTW, there are temp limits for charging both NiMH and lithium-ion rechargables--they should be kept between 32F (0C) and 113F (45C) when charging. The discharge range is larger. https://batteryuniversity.com/index.php/learn/article/charging_at_high_and_low_temperatures

Doug