NiMH vs nicad vs alkaline

pessimist

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I have a handheld ICOM vhf. It has it's own charger which has a switch for alkaline or nicad batteries. Sadly I have only NiMH rechargeable to hand. Will either setting suffice or do I have to use the mains charger which has an NiMH setting? TIA Colin
 

VicS

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I have a handheld ICOM vhf. It has it's own charger which has a switch for alkaline or nicad batteries. Sadly I have only NiMH rechargeable to hand. Will either setting suffice or do I have to use the mains charger which has an NiMH setting? TIA Colin

There is no straight answer as to whether or not a NiCd charger will be suitable for NiMH batteries. From a battery suppliers website:

Can I use an older NiCd battery charger to charge NiMH batteries?

The answer to this question depends on the type of NiCd charger. Depending on the type of NiCd charger you have, the older NiCd charger may undercharge NiMH batteries (most likely), it may overcharge them (less likely), or it may charge NiMH batteries properly (but it's not likely to do so automatically and could take a very long time). Let's take a look at the three cases.

Many of the older NiCd chargers are the simple timed type charger which will charge batteries for a fixed amount of time and then shut off. Unfortunately, since NiCd batteries have a much lower capacity than NiMH batteries, the timer is likely to shut off long before the NiMH batteries are fully charged. This won't harm the batteries, but the NiMH batteries won't be fully charged since the timer will have stopped the charge cycle too soon.

Also common among older NiCd chargers are the so called "overnight" chargers which charge batteries at a low rate as long as the charger is plugged in. This type of charger can fully charge NiMH batteries, but it might take a very long time to do so. It's possible that an old NiCd charger could take as long as 48 hours to fully charge new high capacity NiMH batteries! This type of charger is not likely to damage NiMH batteries unless the batteries are left in the charger for weeks at a time, but it may not be very convenient to use. If you have this type of charger you can get an idea of how long you'll need to charge your batteries by using the calculator found above.

The final possibility is that the older NiCd charger is a rapid charger that will charge NiMH batteries but will not have the necessary circuitry to stop the charge cycle once the NiMH batteries are fully charged. If the NiCd charger is designed to charge batteries in less than two hours it may be this type. In this case the risk is that the older charger will overcharge NiMH batteries. This will be apparent if the batteries get very hot during the charge cycle. (It is normal for NiMH batteries to get warm as they become fully charged, especially in a rapid charger). If the NiMH batteries get too hot to handle and stay that way for more than 20 or 30 minutes, then the NiCd charger is most likely overcharging the NiMH batteries and may shorten their life. You would be most likely to encounter this type of charger if the charger was designed for rapid charging radio control (RC) vehicle batteries. We would recommend that you not use an NiCD rapid charger to charge NiMH batteries.


In the long term unless this radio is heavily used I would go for alkaline batteries. Not rechargeable maybe but they have a good capacity and a long shelf life meaning you can keep a stock of spares to hand.

Li-ion are the only rechargeables worth considering IMHO.
 

TQA

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Use the mains charger.

The algorithms used by the chargers to detect full charge is different for NiCad and NiMH. This is not so critical if you charge at a low rate normally 1/10th of capacity. If it is a "fast" charger running at 1/2 capacity or greater it does matter as the NiMH can overheat and may vent catastrophically.

I have around both for years in RC equipment and have seen quite a few cases of overheating and the magic smoke escaping when fast chargers are used.
 

William_H

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Just in case Vic's satement that "Li-ion rechargeable batteries are the only ones worth considering" causes confusion. The rechargeable Li-ion batteries although in some cases come in AA physical size they are about 3.7 volts per cell so not a replacement for 1.2 volt NiMh or Nicad. Recharging is completely different also.
Not to be confused with lithium AA batteries non rechargeable which are 1.5 volts and very good.
regarding recharging NiMh it would good for the OP to know what kind of charger design and particularly what charge current it will give. he may be able to insert a milliampmeter (digital volt meter) between the bateries to find charge current on various settings. A rate of milliamp hour rating divided by 10 or less is fairly safe for a recharge period of 14hrs. However it is most likely the newNiMh batteries have a lot greater milliamp hour rating so might need to be charged for a lot longer. even up to sweveral days.
good luck olewill
 
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Just in case Vic's satement that "Li-ion rechargeable batteries are the only ones worth considering" causes confusion. The rechargeable Li-ion batteries although in some cases come in AA physical size they are about 3.7 volts per cell ...

You can get dummy AA type batteries, so you can use a single Li-ion for every pair. Never tried it though.
 
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