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Do Ni-MH batteries have memory effect?

Technically, NiMH batteries do not have a memory effect. However NiMH batteries can experience voltage depletion, also called voltage depression, similar to that of NiCd batteries, but the effect is normally less noticeable.

To completely eliminate the possibility of NiMH batteries suffering any voltage depletion effect manufacturers recommend an OCCASIONAL, complete discharge of NiMH batteries followed by a full recharge. NiMH batteries can also be damaged by overcharge and improper storage.

Most users of NiMH batteries don't have to be concerned with this voltage depletion effect.

But if you use a device say a flashlight, radio, or digital camera for only a short time every day and then charge the batteries every night, you will need to let the NiMH batteries run down occasionally.

Will a 1.2v battery work the same as a 1.5v battery

There are a couple of cases where their actual voltage difference may be important to you. In the case of a device like a radio, where a higher voltage can mean a stronger signal, a fresh alkaline battery may be more desirable - but more expensive - than a rechargeable NiMH battery. This is also true for a tourch, which will be brighter with the initial higher voltage of alkaline cells. This minor difference may not be important to you and is probably offset by the much lower cost of operating NiMH batteries. And keep in mind that the alkaline battery only has a higher voltage when it is fully charged. Once it gets to 50% capacity or less, it will be delivering a lower voltage than a NiMH battery.

The one time when the voltage difference of the two is important would be in the case of a device that checks the voltage of a battery to estimate the amount of charge left on the battery. Because the voltage of an alkaline battery drops at a very predictable rate it's possible to estimate the amount of capacity left in an alkaline battery based solely on its voltage. 1.5 volts - fully charged, 1.25 volts - 50% charged, 1.0 volts - almost fully discharged. But a NiMH battery stays at about 1.2 volts until it is nearly completely discharged. This makes it almost impossible to know the amount of capacity left based on its voltage alone. When a device that's using NiMH batteries indicates the battery is low, it's time to change the batteries now!

Do Ultra or Advanced Formula batteries last longer

Yes, for high drain applications Duracell Ultra and Energizer Advanced Formula batteries do last longer than standard alkalines. Unfortunately, they only last about 30% longer. So instead of lasting for say 15-25 images they might last for 20-40. That's a little better but it's still pretty poor, especially considering that these new style alkalines cost as much as £1.50 each. Rechargeable NIMH is the better choice for high drain applications. They last much longer on a single charge and don't have to be discarded after a single use.

Why do digital camera's use so many alkaline batteries

Alkaline batteries were not designed to meet the very high power demands of today's electronic devices. Alkaline batteries have a high rated capacity, but they can only deliver their full capacity if the power is used slowly.

Electronic devices such as digital cameras place a high power drain on batteries, so it is much better to use rechargeable NiMH batteries for these type of devices.

Lithium batteries which also work well in high drain applications but they are expensive and are not designed to be recharged.

What is the self discharge rate of a NiMH battery?

The rate of self discharge for any battery depends on the temperature at which it's stored. Stored at 70 degrees F (20 C) NiMH batteries will lose up to 40% of their charge within a month. If they are stored at a higher temperature, they will self discharge at an even higher rate. Stored at a lower temperature they self discharge at a lower rate.

Can I substitute a higher mAh battery for a lower one?

Yes, for most high drain electronic applications NiMH batteries are ideal substitutes and you needn't worry about the apparent voltage differences. Even though alkaline batteries are rated at a nominal 1.5 volts, they only deliver 1.5 volts when they are fully charged. As they begin to discharge the voltage of alkaline batteries continuously drops. In fact, over the course of their discharge, alkaline batteries actually average about 1.2 volts. That's very close to the 1.2 volts of a NiMH battery. The main difference is that an alkaline battery starts at 1.5 volts and gradually drops to less than 1.0 volts. NiMH batteries stay at about 1.2 volts for most of their discharge cycle.

There are a couple of cases where their actual voltage difference may be important to you. In the case of a device like a radio, where a higher voltage can mean a stronger signal, a fresh alkaline battery may be more desirable - but more expensive - than a rechargeable NiMH battery. This is also true for a torch, which will be brighter with the initial higher voltage of alkaline cells. This minor difference may not be important to you and is probably offset by the much lower cost of operating NiMH batteries. And keep in mind that the alkaline battery only has a higher voltage when it is fully charged. Once it gets to 50% capacity or less, it will be delivering a lower voltage than a NiMH battery.

The one time when the voltage difference of the two is important would be in the case of a device that checks the voltage of a battery to estimate the amount of charge left on the battery. Because the voltage of an alkaline battery drops at a very predictable rate it's possible to estimate the amount of capacity left in an alkaline battery based solely on its voltage. (1.5 volts - fully charged, 1.25 volts - 50% charged, 1.0 volts - almost fully discharged). But a NiMH battery stays at about 1.2 volts until it is nearly completely discharged. This makes it almost impossible to know the amount of capacity left based on its voltage alone. When a device that's using NiMH batteries indicates the battery is low, it's time to change the batteries now!

What does mAh when buying batteries stand for?

mAh stands for milli Ampere hour or milli Amp hour. It is a measure of a battery's energy storage capacity. If you think of a battery as a small fuel storage tank, which in a sense it is, mAh a measure of how much "fuel" the battery holds. With a battery the higher the mAh rating the more electrical energy it can store.

Different types of batteries use different methods to measure mAh so comparing the mAh rating of one type of battery, say an alkaline battery to another say an NiMH battery, is not always meaningful.

However, in general, the mAh rating of a battery is a quick way to compare the relative energy storing capacity of one battery to another battery of the same type.

How many times can I charge an Ni MH battery?

AA2100mAh & AA 2300mAh can be charged up to 1000 times.

AA 2500mAh & AA 2700mAh has a greater capacity but can be recharged approx up to 700 times.

Capacity improvement will always decrease the number of cycles.
Every cell on the market above 2300mAh will have below 1000 charge cycles

Can differing battery capacity cells be charged at once?

No - It is not recommended to mix Ni MH battery capacitys when charging.
Use the same capacity for a single charge.