Can Ni-Cad batteries be replaced with NiMH???

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madabouttheboat

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I have a Handheld VHF which doesn't hold a charge at all.

The battery pack states that it is 7.5V Ni Cad

Upon opening it up. it contains 6 x AA size rechargeables. That makes them 1.25v each.

The charger states that it outputs 9Vdc 100mA.

If I was to replace these batteries with NiMH would the charger charge them and would there be any other problems?

Cheers all
 
I think the charge regime for NiMH is different than NiCad.
But why dont you just use new NiCad's?? With the right treatment they should last well.
 
I was thinking that NiMH were a better battery. No memory effect, bigger capacity etc. I may be wrong on that!

Many domestic chargers for AA rechargeable batteries seem to state that they can recharge NiCad or NiMH batteries but they may have a selector switch on them. I don't have one to hand so can't check. Anyone know?

Cheers
 
[ QUOTE ]
I have a Handheld VHF which doesn't hold a charge at all.

The battery pack states that it is 7.5V Ni Cad

Upon opening it up. it contains 6 x AA size rechargeables. That makes them 1.25v each.

The charger states that it outputs 9Vdc 100mA.

If I was to replace these batteries with NiMH would the charger charge them and would there be any other problems?

Cheers all

[/ QUOTE ]

The experts will give all sorts of info why, why not etc. Practical answer ? You will most likely find the old NiCd's are around 600 -800mA size. You can safely increase that to the largest capacity you can find AND change to NiMH giving an incredible improvement in performance - your operating battery time will be much longer although charge time will be longer. You can safely charge at any level of discharge, without need for charge management ie. discharge then charge.

So simple answer is - Yes change to NiMH and Yes original charger will charge them. (Some will argue with this but Hubby has changed everything of ours over to higher capacity NiMH as NiCD's fail and we have much better gear as a result).
 
I have not done it to a VHF but have put a new AA size NiMH battery into an electric razor to replace NiCad, and done the same to a cordless telephone (2XAAA) an old battery drill (6 X C size). No problems with any of them. The razor does get slightly warm on charge, but it works just fine.
 
Yes, the only trouble is that the batteries will take forever to charge - I have a 1994 vintage VHF that used to charge in 10 hours when it had 600ma/H nicads and now it has 2800ma/H NiMH it takes about 2 days , but then I only have to charge it about a quarter as often. The only real problem is NiMH batteries self-discharge fairly fast, and that old NiMH fade away differently (get feeble, high resistance, lose capacity) to NiCd (lose capacity or just short themselves when flat), so you might be able to transmit on old NiCd for a short time but not manage anything on old NiMH.
 
Quote "The only real problem is NiMH batteries self-discharge fairly fast,"

My Standard Horizon handheld VHF has NiMH batteries. I left it on the boat, only part charged, last October. I returned at the end of March to do the antifouling and launch the boat and it was working. I did not charge it up, because I did not use it much, and it was still working in June when I returned to the boat. I make that about 8 months without self discharge. It is a different matter if you have a VHF with a so called soft on-off switch, as some makes do not fully switch off, but continue to drain their batteries slowly.
 
yes, its fine. Check the capacity of the batteries you buy and divide by 100(your charger) to give a guide to the charge time.
You can get fast chargers which will do the trick in 20 mins or so, but just note that Nicad and Nimh have different charge recognition, so ensure any fast charger is suitable for Nimh.
Nicads still have their place.. they are cheap and are better for high drain such as power tools.
 
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.......and divide by 100(your charger) to give a guide to the charge time........

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Why 100 ? Actually you divide battery size ie 2000 mA/Hr by charger charge rate ie 500 mA ... maths gives 4 hrs, but will be more like 6 - 7 hrs with losses taken into account.
The benefit you will get if you increase battery size is the charger will not overcharge the batteerys and can literally be left maybe indefinitely.

[ QUOTE ]
You can get fast chargers which will do the trick in 20 mins or so, but just note that Nicad and Nimh have different charge recognition, so ensure any fast charger is suitable for Nimh.

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If you go fast charger then you must not exceed charge required time based on amount of time battery discharged. So as you can realise easily is not a good way to go. Keep to low charge rate chargers and the high boosted to others !

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Nicads still have their place.. they are cheap and are better for high drain such as power tools.

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True but generally not a consideration for most applications. NiCd's must be discharged near fully before charging to protect capacity, unless on full charge trickle.

Some time ago we were very close friends of a Tech. Guy at M******* Batteries and it was very interesting listening to roles and uses of various types of batterys. One was the problem that develops from partial discharge and charge cycles of NiCD's when repeated too often. He produced graphs and test data that showed it to be fact, not many people need proof other than their own ! Pity we can't put hands on it now - but it was some years ago.
 
I have the same problem. It's a Garmin VHF 725e. The rechargable pack is also 6 NiCd which on a good day give 7.2 volts - not enough to satisfy the device and it always gives the flat battery beeps when you turn it on.

The separate battery holder takes 6 AA disposable cells which are nominally 1.5 volts - 9 volts altogether which is enough to tell the battery state indicator it has a good battery and everything works fine. Rechargable AA NiMH batteries (1.2v) in the holder give the same indication as the rechargable pack.

Thing is though, even when the indicator says the battery is flat, it still works OK.

Bit of a design fault I'd say!
 
I personally feel that rechargeables be they Ni-Cd or NiMH are a dead loss unless they are in equipment that is seeing a lot of use and are always recharged promptly.

The memory effect of Ni-Cds is well known meaning that they should be discharged before recharging. Some say that's a myth, others say it applies to NiMHs as well.

Neither Ni-Cd nor NiMH appreciate being left in a discharged state.

Both loose their charge fairly quickly although Ni-Cd may be worse than NiMH

For equipment that has infrequent or intermittent use or which is expected to survive without regular charging alkaline disposable batteries are to my mind a better bet. They may have a slightly lower capacity than some of the modern NiMHs but they have a long, long shelf life. so a good stock can be bought and maintained.
 
[ QUOTE ]
I have the same problem. It's a Garmin VHF 725e. The rechargable pack is also 6 NiCd which on a good day give 7.2 volts - not enough to satisfy the device and it always gives the flat battery beeps when you turn it on.

The separate battery holder takes 6 AA disposable cells which are nominally 1.5 volts - 9 volts altogether which is enough to tell the battery state indicator it has a good battery and everything works fine. Rechargable AA NiMH batteries (1.2v) in the holder give the same indication as the rechargable pack.

Thing is though, even when the indicator says the battery is flat, it still works OK.

Bit of a design fault I'd say!

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Nominal and actual working voltage are 2 completely different beasts and are also different relations depending on the batterys used.
Dry-cells show 1.5V on no load, but drop of sharply to 1.2V or less under load. Rechargeables and here we can lump all together, NiCD, NiMH and LiIon, show 1.25V on no load, (some may show 1.3V) and when put under load will exhibit nearly same.
The stability of voltage of rechargeables is remarkable and is why if you compare a Dry-cell pack and a rechargeable pack for many items, the dry-cell pack has 1 more cell than the rechargeble.
Battery state meters do not like rechargeables as they do not have high no-load voltage, also have near horizontal voltage line during discharge giving no indication of charge left for meter to use.
Your finding VHF works fine on the rechargeables despite meter display is not unusual and is explained by the above.
 
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