Charging NiMh batteries when not completely discharged

The aaa alkaline batteries went out on my tv remote.

I decided to use my NiMh UBL aaa batteries. 1100 mAh.

They are currently showing 1.31 volts.

And they work ok in the remote as is.

My charger is the manual type.

It charges that type at 150 mA.

I want them fully charged since they are 1.2 volts versus 1.50 for the alkaline.

I would like to know how much longer to charge them.

Thanks, Andy

Reply to
AK
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** The correct procedure is to discharge the cells fully and then apply a full recharge cycle - 8 hours in your case.

If you must recharge partly discharged cells, then it takes whatever time needed until their temperate just starts to rise. Constant monitoring by you is needed.

... Phil

Reply to
Phil Allison

I have no way of monitoring temp.

How do I fully discharge the cells manually?

Andy

Reply to
AK

If they are unused, it is best to charge low self-discharge NiMH every nine to twelve months. Do NiMH batteries need to be completely discharged before charging? No, NiMH batteries do not have a memory. They can be charged without adverse effect at any point regardless of their state of charge.

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Get a quality charger that monitors each battery under charge individually with an indicator for each cell to tell you when it is recharged.

Monitoring temperature is over-kill IMO and not the best method. It is too dependent on ambient temperatures, air flow, etc..

By all means get the batteries that are low self-discharge types. (sold as "pre-charged")

Old Nickel Cadmium cells required discharging to get the full capacity out of them.

Reply to
default

Thanks default.

My EBLs were low self discharge.

Andy

Reply to
AK

EBL is what I've been buying and get good results with them. Eneloop are excellent too but cost more. I just bought some Amazon branded batteries to see if they are any good (but the price wasn't that much better than EBL).

Awhile back, after getting frustrated with rechargeable AA performance, I rigged a dummy load across a battery holder and bought a few cheap quartz clocks to see which of the odd collection of batteries I had on hand still could hold a decent charge. The clocks stop working when the voltage gets down to ~.7V and records the hours takes to get there.

Reply to
default

Interesting results.

Andy

Reply to
AK

I thought the subject was batteries, not cells.

When considering discharging, there is a very significant difference between cells and batteries.

Fully discharging a cell with a resistor is relatively safe, whereas fully discharging a battery that way *will* cause the weakest cell to be reverse charged - and damaged.

Reply to
Tom Gardner

Yeah, I conflate cell with battery, as do a lot of people.

AND that idea that the weakest cell suffers in a battery would also hold true for the cheap chargers that charge cells by the pair. No charging takes place unless there are two cells and then they are charged in series - that seems like a good way to screw up batteries.

Reply to
default

No, not necessarily.

Different cells *will* have different capacities due to manufacturing tolerances. Discharging them in series *will* lead to the cell with the smaller capacity becoming reverse charged - and damaged.

Providing that the current/voltage is within the specified trickle charging limits, if you charge in series then one cell will become fully charged before the other but overcharging shouldn't damage it.

Reply to
Tom Gardner

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** When I was involved in electric car racing, the favourite way to discharge a 7.2V NiCd pak was to use a small, 12V lamp.

When the lamp dimmed, time was up. Immediate recharge prevented the harm that sometime happens to a reversed cell.

The risk is much greater with paks that contain many cells, the OP has a two cell pack so the risk is minimal.

... Phil

Reply to
Phil Allison

Not a surprise; alkaline cells when fresh are 1.5V, but are useful down to about 1V. NiCd and NiMH are 1.2 to 1.4V fresh-charged, useful down to about 1V. Li nonrechargeables are 3.6V fresh, useful down to 3.0V (so can replace a 4.5V alkaline clock battery, or two in series can replace a 9V which has 6 alkaline cells)

Don't use rechargeables for best shelf life, but for best total life.

Mainly, your remote control is inert (it gets used in subsecond bursts when you press a button). The self-discharge when not in use (and higher purchase price) make rechargeables a questionable fit for that application.

Reply to
whit3rd

I would think in terms of overall costs, that nimh would be cheaper than buying alkaline aaa batteries. My "alkies" last about 6 months. I have charged the nimh ones about 3 times. My charger charges them separately.

It would help me find relevant replies if so many were not littered with arguments and cussing. Thanks,Andy

Reply to
Andy

I agree. The price on rechargeables has come down, chargers have gotten much better, and the low self-discharge make them hard to beat. (and you aren't storing a lot of alkaline batteries so you have them on-hand when you need them). (I store batteries in the refrigerator so space counts)

Amazon has their house-brand rechargeable for ~$12 for 12 AAA batteries, and EBL $24 for 16 AAA and an eight station smart re charger as a package deal. Eneloop is $28/12 batteries.

Amazon house brand alkaline is $20/100 AAA size, and name-brand ~$40/100 (sounds like a 1-2 year supply for me)

Reply to
default

** Then you would be thinking wrong.

It is ONLY in high usage and high current applications that re-chargeables come out the winner.

For items like remotes, clocks, DMMs, rarely used torches and any low usage item - forget NiMH cells.

  • It would help even more if the half witted, half baked trolls who think they own the NG would kindly piss off.

.... Phil

Reply to
Phil Allison

That it would, PHIL.

Reply to
default

Yeah, FUCK OFF PHIL.

Reply to
Al

I use Eneloop calls in my remotes and not just for the savings or reduced waste over using throw-away cells. I've had more than one remote damaged by leaking alkalines and am yet to see an Eneloop leak so there's that...

I use a Maha One charger / conditioner which is also great for matching cells if you need to run them in series.

--
Shaun. 

"Humans will have advanced a long, long way when religious belief has a cozy little classification  
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Reply to
~misfit~

I already had them, so decided to go ahead and use em.

Andy

Reply to
AK

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