# How to store NiMh and NiCd batteries?



## lovefenix (Dec 9, 2008)

Hi.

I have some questions about storing batteries.The information on the net isn`t clear.Everybody says something different and it gets confusing.

1. Why do experts recommend that you discharge NiCd batteries when you don`t use them for a long time,(eaven if you use it often)?

They don´t explain if you have to discharge them to zero or just to 0,9V.

2. Does charging a NiMh battery to 50% slows the self discharge rate compared to a full charge? If so.By how much?

3.When you buy a NiMh battery.They are supposed to come with an empty charge.Does the lifetime of the battery start counting from the *first time *you charge them?How many years can they be stored new without significant impact on its performance?

4.Is it better to charge a new pack only when needed?It`s the shelf life of a new empty battery the same as one that was charged and discharged just one time and put to rest?
Will I have to charge that battery like once per year so that it does´t get ruined or something?

5.There is a date code in my eneloop batteries.It says "06-08TB".Is the first number the year or the month it was made?

Is it me or a lot of eneloop batteries start with 06?:thinking:

Thanks all.


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## Mr Happy (Dec 9, 2008)

lovefenix said:


> Hi.
> 
> I have some questions about storing batteries.The information on the net isn`t clear.Everybody says something different and it gets confusing.


I'll see if I can help.



> 1. Why do experts recommend that you discharge NiCd batteries when you don`t use them for a long time,(eaven if you use it often)?
> 
> They don´t explain if you have to discharge them to zero or just to 0,9V.


NiCd batteries perform best if they are fully discharged before being recharged. This is due to the so-called "memory effect". What it means in practice is that cells that are frequently topped up without being discharged will tend to develop a lower capacity to hold charge. If cells get into this state, they can usually be returned to normal operation by putting them through one or more full discharge/recharge cycles. This is what the "refresh mode" on some chargers is for.

NiCd batteries are different in some ways from NiMH batteries. For example, you can discharge a NiCd cell right down to 0 V and store it that way indefinitely. However, NiMH cells must not be discharged below 1.2 V resting voltage. If you discharge them down to 0 V for a long period, they will be damaged.



> 2. Does charging a NiMh battery to 50% slows the self discharge rate compared to a full charge? If so.By how much?


The self discharge is fastest at a full charge, and is slower at a 50% charge. However, you may as well charge them to 100% and then use them as soon as convenient. There is no point only charging to 50%



> 3.When you buy a NiMh battery.They are supposed to come with an empty charge.Does the lifetime of the battery start counting from the *first time *you charge them?How many years can they be stored new without significant impact on its performance?


This depends on whether it is an old-style regular NiMH or a new-style low self discharge ("pre-charged", LSD) NiMH, like Eneloops.

All NiMH cells are given some charge at the factory, since storing an NiMH cell empty of charge will damage it. This means that when you buy NiMH batteries, you should try to make sure they are as freshly manufactured as possible. If they have been stored in a warehouse for two years before you receive them, they might already be damaged from self-discharge below a safe level (note: this does not apply to LSD cells so much).

Also, old-style regular NiMH cannot be stored for years without maintenance. Every six months at least, they should be put through a refresh cycle and then given a moderate charge before being put back into storage.



> 4.Is it better to charge a new pack only when needed?It`s the shelf life of a new empty battery the same as one that was charged and discharged just one time and put to rest?
> Will I have to charge that battery like once per year so that it does´t get ruined or something?


As mentioned above, a regular NiMH battery will start to get damaged if you don't touch it for a year or more. When you get new NiMH cells you should immediately take them out of the packaging and put them through a charge/discharge/charge cycle. Then you should either use them, or refresh them every six months.

Again, this doesn't apply so much to the new breed of LSD batteries. These apparently can be stored for two or more years without damage. Nobody has found out exactly how long yet.



> 5.There is a date code in my eneloop batteries.It says "06-08TB".Is the first number the year or the month it was made?
> 
> Is it me or a lot of eneloop batteries start with 06?:thinking:


Yes, this means August 2006. For some reason, a very large number of 2006 Eneloops were imported into the USA and are still reaching retail channels even now.


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## The Light! (Dec 10, 2008)

Mr Happy said:


> NiCd batteries perform best if they are fully discharged before being recharged. *This is due to the so-called "memory effect"*



I'm afraid I have to disagree with you Mr Happy... I thought NiCads had a memory effect till I asked it on THIS thread on CPF. Turned out we are both wrong... NiCads have about as much memory as NiMH!  
Lovefenix, read through the thread, it has some very interesting info + links on how to treat NiCads so that they last for years to come! 
Hope this helps!


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## Eugene (Dec 10, 2008)

lovefenix said:


> Hi.
> 
> 5.There is a date code in my eneloop batteries.It says "06-08TB".Is the first number the year or the month it was made?
> 
> ...




Remember eneloops are not the same as traditional NiMH so the storage practices will be different. You mentioned that NiMH should come discharged for example, Eneloops come charged. I top off my eneloops maybe once every 6 months or a year or after each use and leave them that way.


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## Mr Happy (Dec 10, 2008)

The Light! said:


> I'm afraid I have to disagree with you Mr Happy... I thought NiCads had a memory effect till I asked it on THIS thread on CPF. Turned out we are both wrong... NiCads have about as much memory as NiMH!


I thought someone might pick up on that 

Actually you are right that NiCd have as much memory as NiMH -- they both have a "memory effect"!

I put the term "memory effect" in quotes, because it does indeed exist, though not quite in the way that is often supposed. What happens with both NiCd and NiMH cells is that if you keep them fully charged by regular topping off then they will begin to exhibit an apparent loss in capacity. This is a temporary change in the internal cell chemistry that can be reversed by putting the cell through a refresh cycle of full discharge followed by a full charge, repeated maybe more than once. It is the reason why chargers such as the LaCrosse BC900 or Maha C9000 provide a refresh function.

A good guideline to keep both NiCd and NiMH cells performing well is to put them through a full refresh cycle every 3-6 months, and if possible to let them become fully drained in use before recharging them, rather than frequently topping them off. Topping off has a second problem in that it subjects the cell to an overcharge condition more frequently. Cells are designed to take a certain amount of overcharge in normal use, but NiMH in particular can be harmed by excessive overcharging.


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