Can Eneloops be "topped up"?
- Thread starter David18
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Max_Power
Enlightened
Yes, eneloops can be topped off at any time. They are pretty forgiving.
TranceAddict
Newly Enlightened
all nimh cells inherit memory effect. but thats not a big deal, just refresh them every half year will do.
Is that true? I thought that true memory was limited strictly to NiCads, and even then, only seen under very specific conditions.
Do NiMh exhibit something similar?
--flatline
45/70
Flashlight Enthusiast
NiMH"s can suffer from so called "memory" effect, it's just that they are only prone to it about half as much. When you see NiMH advertisements claiming that they don't, it's just marketing B.S.
Dave
TakeTheActive
Enlightened
Beware the 'Null Zone'!
AFAIK, most Smart Chargers have a 'Null Zone' (a period where they ignore all termination signals in order to avoid false terminations during the beginning of a charge cycle).
If your cell is completely 'Topped Off' while the charger is 'not looking', the cell can then be overcharged.
A recent discussion of this topic took place in: Test for how well batteries suit your charger
It depends on how SLIGHT the discharge is and the size of the charger's 'Null Zone'.
AFAIK, most Smart Chargers have a 'Null Zone' (a period where they ignore all termination signals in order to avoid false terminations during the beginning of a charge cycle).
If your cell is completely 'Topped Off' while the charger is 'not looking', the cell can then be overcharged.
A recent discussion of this topic took place in: Test for how well batteries suit your charger
TakeTheActive
Enlightened
Apollo Cree
Enlightened
Memory effects
Note: this applies to NiCd or NiMH batteries only. Lead or Lithium cells are different.
First some terminology. A battery is multiple cells. AA, AAA, C, or D cells are single cells. For NiCd or NiMH, anything between 1 to 1.5 V is a single cell. Anything 2 volts or more is a "battery" of individual cells. Technically, a AA battery is not a battery, it's a cell.
The memory effect is mostly a myth. Yes, it can happen, but it's so difficult to make happen that 99% of us have never seen it.
If you DO somehow manage to see the memory effect, a good charge with a slow trickle charger and a modest discharge will fix it.
What I have seen is the "dead battery" effect. Every time I've heard people claiming that they have "memory effect" batteries, what they described was NOT memory effect.
Sometimes the batteries simply die on you. However, you can cause them to die yourself. How do you kill a battery?
1) Reverse charge it. If you have a multi-cell battery, or stack more than 1 cell and charge them in series, you can harm it by discharging it. This is one reason why it's a BAD idea to deeply discharge a multi-cell battery.
How does this happen? If one cell drops to zero voltage before the rest, the good cells will push current "backwards" through the cell, reverse charging it. This causes irreversible damage.
If all the cells in a battery are exactly identical, you won't reverse charge them. They'll all discharge to zero at the same rate.
Don't deeply discharge a multicell battery, or a device that uses multiple cells.
If you're using multiple cells, it's best to use them in groups that are all from the same original package, the exact same model and type, and always use them and charge them in the same group. Don't mix new and old batteries, even if they're the same type and model.
Even if you fully charge the batteries, if you let them sit for a long time before using them, one will self discharge faster than the others, and increase the chance of revers charge.
If you MUST deeply discharge a battery, you need to discharge one cell at a time. Individual AA cells or AAA cells are OK. If it's a battery pack, full discharge is a no-no unless you can clip on to individual cells and discharge them independently.
If you're going to discharge a multicell battery to keep it happy, be sure it's freshly charged, preferably with a slow charger or left overnight or longer on a smart charger that does trickle charge after it shuts off. This makes it less likely that one cell has self-discharged itself to the point where it will reverse charge.
I'm not recommending deep discharge, but this is how to do it without destroying them by reverse charging them.
By the way, deep discharge is ALWAYS a bad idea for a lead acid battery, even "deep cycle" batteries. "Deep cycle" batteries are simply damaged less by deep discharge than "starter" batteries.
2) Overcharge
A "dumb" battery charger may damage a rechargeable battery. Dumping too much current too fast into a rechargeable cell after it's charged will damage it.
The effect is less with smaller currents. However, even a rather small current will eventually damage a battery if you leave it charging all the time.
Some "smart" chargers hit the battery with a high current until they think it's fully charged and then drop back to a trickle charge. In concept, this gives a "perfect" recharge.
In practice, sometimes the charger is not as smart as it thinks it can and it will overcharge the battery before it shuts off.
If you only slightly discharge the battery, "smart" chargers are more likely to do this. "Fast" chargers are more likely to do this.
3) Reverse charging and overcharging are something that pretty much all the experts agree on. I think a lot of people also have what I call "pathological smart charger syndrome."
What I think happens is this. One cell in a pack has a lower amount of charge (or something.) The cell runs down quickly while the other cells are still nearly full. When you try to recharge the battery, the "smart" fast charger somehow shuts off when some of the cells are fully charged and the weaker cell is still mostly discharged.
How to fix this? If you try to completely discharge the battery pack, you will reverse charge and ruin the weak cell. If you can discharge the cells individually that will work. You can also finally charge the weak cell, if you have a slow trickle charger. Sometimes a little "playing around" with the charge cycles will fix it, but if you simply take out the "charged" battery pack and start another charge cycle, the "smart" charger may damage some of the cells via overcharge.
4) I think a lot of rechargeable battery failures are not due to anything the user has done. It just happens.
---
I like to use a smart charger that takes 6 hours or more. I will also use a trickle charger, but not leave it on more than a day or so.
Once again, lithium rechargeables are entirely different. I'm always a bit afraid they'll explode if I monkey with them.
Lead acid batteries also require entirely different charging procedures.
Note: this applies to NiCd or NiMH batteries only. Lead or Lithium cells are different.
First some terminology. A battery is multiple cells. AA, AAA, C, or D cells are single cells. For NiCd or NiMH, anything between 1 to 1.5 V is a single cell. Anything 2 volts or more is a "battery" of individual cells. Technically, a AA battery is not a battery, it's a cell.
The memory effect is mostly a myth. Yes, it can happen, but it's so difficult to make happen that 99% of us have never seen it.
If you DO somehow manage to see the memory effect, a good charge with a slow trickle charger and a modest discharge will fix it.
What I have seen is the "dead battery" effect. Every time I've heard people claiming that they have "memory effect" batteries, what they described was NOT memory effect.
Sometimes the batteries simply die on you. However, you can cause them to die yourself. How do you kill a battery?
1) Reverse charge it. If you have a multi-cell battery, or stack more than 1 cell and charge them in series, you can harm it by discharging it. This is one reason why it's a BAD idea to deeply discharge a multi-cell battery.
How does this happen? If one cell drops to zero voltage before the rest, the good cells will push current "backwards" through the cell, reverse charging it. This causes irreversible damage.
If all the cells in a battery are exactly identical, you won't reverse charge them. They'll all discharge to zero at the same rate.
Don't deeply discharge a multicell battery, or a device that uses multiple cells.
If you're using multiple cells, it's best to use them in groups that are all from the same original package, the exact same model and type, and always use them and charge them in the same group. Don't mix new and old batteries, even if they're the same type and model.
Even if you fully charge the batteries, if you let them sit for a long time before using them, one will self discharge faster than the others, and increase the chance of revers charge.
If you MUST deeply discharge a battery, you need to discharge one cell at a time. Individual AA cells or AAA cells are OK. If it's a battery pack, full discharge is a no-no unless you can clip on to individual cells and discharge them independently.
If you're going to discharge a multicell battery to keep it happy, be sure it's freshly charged, preferably with a slow charger or left overnight or longer on a smart charger that does trickle charge after it shuts off. This makes it less likely that one cell has self-discharged itself to the point where it will reverse charge.
I'm not recommending deep discharge, but this is how to do it without destroying them by reverse charging them.
By the way, deep discharge is ALWAYS a bad idea for a lead acid battery, even "deep cycle" batteries. "Deep cycle" batteries are simply damaged less by deep discharge than "starter" batteries.
2) Overcharge
A "dumb" battery charger may damage a rechargeable battery. Dumping too much current too fast into a rechargeable cell after it's charged will damage it.
The effect is less with smaller currents. However, even a rather small current will eventually damage a battery if you leave it charging all the time.
Some "smart" chargers hit the battery with a high current until they think it's fully charged and then drop back to a trickle charge. In concept, this gives a "perfect" recharge.
In practice, sometimes the charger is not as smart as it thinks it can and it will overcharge the battery before it shuts off.
If you only slightly discharge the battery, "smart" chargers are more likely to do this. "Fast" chargers are more likely to do this.
3) Reverse charging and overcharging are something that pretty much all the experts agree on. I think a lot of people also have what I call "pathological smart charger syndrome."
What I think happens is this. One cell in a pack has a lower amount of charge (or something.) The cell runs down quickly while the other cells are still nearly full. When you try to recharge the battery, the "smart" fast charger somehow shuts off when some of the cells are fully charged and the weaker cell is still mostly discharged.
How to fix this? If you try to completely discharge the battery pack, you will reverse charge and ruin the weak cell. If you can discharge the cells individually that will work. You can also finally charge the weak cell, if you have a slow trickle charger. Sometimes a little "playing around" with the charge cycles will fix it, but if you simply take out the "charged" battery pack and start another charge cycle, the "smart" charger may damage some of the cells via overcharge.
4) I think a lot of rechargeable battery failures are not due to anything the user has done. It just happens.
---
I like to use a smart charger that takes 6 hours or more. I will also use a trickle charger, but not leave it on more than a day or so.
Once again, lithium rechargeables are entirely different. I'm always a bit afraid they'll explode if I monkey with them.
Lead acid batteries also require entirely different charging procedures.
