NICAD & NIMH Power Tool Battery Repair Service

Cordless Power Tool Battery Repair and Reconditioning

Frequently asked Questions

Most Quality power tools on sale now, including DEWALT, BOSCH, MAKITA etc supply 1.3 to 2 Ah (1300 to 2000 mAh) NICAD in their cheaper ranges with NiMH up to 3.5Ah battery packs  for top of the range models. Lithium Ion batteries account for about 70% of new power tools and this is increasing.


Battery Care - What is the best way to look after my battery?

NICAD batteries

The worst thing you can do to a NICAD or to some extent NIMH battery is not use it. Even if a charged battery is stored for extended periods they have a tendency to "Die". Once this has happened, they can be revived but will lose the ability to store a charge for long periods, ie fine after a charge will be good for a few days but will be totally discharged in a few weeks.

If not required for long periods (a month or more), run a discharge/charge cycle if you have a smart charger. If not, run down in a drill etc, then give a full charge and repeat once a month. This will also condition the cells to the same charge level as they discharge at slightly different rates. This is the same as Reconditioning explained below.

They also do suffer from  MEMORY EFFECT  This can be reduced by a charge/discharge cycle on the charger if it has one. If not the best way is to run it down completely on the drill or similar equipment, then re-charge. This is calledRECONDITIONING  which will help to increase the capacity of the battery.

The prime reason is to ensure all the cells start from a discharged state; instead of some cells with a charge and some without any charge, causing an imbalance.

NIMH batteries

Same applies to this type but they are less likely to "Die" than NICAD's. They also require conditioning cycles but not so frequently as NICAD's. For this reason they are better suited for the "occasional" handyman jobs.

For frequent everyday use, either is good but NIMH usually have a higher capacity than Nicad's.

Never leave any power tool battery in  a shed or unheated outhouse during the winter months. Most Winters cold spell kill  many batteries of all types as the electrolyte freeze causing the cells to rupture.


NICAD or NIMH, what is the difference?

There is quite a bit of confusion about the difference. As far as Power tools are concerned - very little. It's the chemical makeup that's different.

NICAD and NIMH cells can be interchangeable (as a set) and most chargers will work the same with either type, as they are Delta T type. These chargers are designed to terminate with an increased temperature at the end of charge and will work on both types. Older type Delta V peak detection NICAD chargers may not work properly with NIMH as the Voltage drop at the end of charge is more subtle and may not be detected, resulting in overcharge. Slow or trickle chargers will work on both but as most NIMH batteries are higher capacity, they need much longer to charge and if left at the same charge time can under-charge the battery.

NIMH batteries should not be charged greater than half the capacity (C) at a constant rate. ie, If the capacity is 3Ah the charge current should not be more than 1.5Amps (in some cases up to C -3A is possible but needs to be tested first). This is because NIMH cells produce heat when charged, unlike NICAD cells, which produce less heat. This can cause the cells to overheat if the current is too high, or terminate prematurely if controlled by a temperature sensing devise.

However most SMART chargers will use a pulsing charge, which will allow a high current with less heat, or fast charge (say at 5 to 10 Amps) for the first stage, then 0.5C for the last stage - or a combination of both.

To find out what your charger type is, check how many connections there are from the charger to the battery. This may involve removing the cover to the charger. If it's only a 2 wire connection, it's either a slow/trickle charger or a Delta V type. If 3 or more connections it's a Delta T type. Nearly all power tool batteries have 3 or more connections, as they are fitted either with a Thermistor or temperature switch (or both). This is to suit most types of charger.

Higher capacities are possible with NIMH type but their disadvantage is leakage. They lose up to twice as much charge in a given time as NICAD batteries. NICAD batteries are more harmful to the environment but not if disposed of properly (recycled). NICAD's can be charged up to 4C but their life is reduced.NICAD vs NIMH

Lithium Ion - Advantages, disadvantages

Advantages are no memory effect, much greater capacity for same weight as Nimh or Nicad. Ability to hold full charge for long periods. Disposal is non toxic.

Disadvantages include - liable to explode if overcharged, or damage if cell voltage drops too low. For power tools this can be an abrupt stop as sensors detect this. Generally not as good power output as Nicad or Nimh (tends to die under heavy loads). Complicated charging circuits with circuit boards inside the battery.

What equipment should I buy - NICAD, NIMH or Li-ION?

My advise would be to avoid Lithium Ion batteries and stick to the traditional HQ NICAD or NIMH type. 

Reason for this is because manufacturers of Lithium Ion batteries have become very clever in their design of protective circuits that are necessary but easy to include extras that prevent repairs, thus ensuring you have to buy a replacement from them at their price - which will be high!

Makita for example on their 14.4V and 18V, 3Ah range the circuit locks up after 750 charges, it will no longer charge on a Makita charger again, regardless if the battery is still good. Or if it detects a fault on the cells, after 3 attempts to re-charge, locks up and will never charge again on a Makita charger, even if the cells have been replaced. There is no way round this and Makita will not even answer queries about it. There are also 3 different types of Li-Ion cells used by various manufactures which are all difficult to obtain in the UK.