Peter Parry wrote:
On Wed, 01 Jul 2009 23:26:11 GMT, "The Medway Handyman"
wrote:

Peter Parry wrote:

NiMH and NiCd have very similar charging and discharge
characteristics. NiMH batteries often come with better quality
chargers and it is this rather than their fundamental
characteristics which make a difference. NiMH have a slightly
higher charge capacity than NiCd for a given weight.

NiMH (Nickel Metal Hydride). These batteries have no memory effect

Neither do NiCd.

Is that so? I've always believed NiCD did have a memory effect.

No, its one of the oldest red herrings going. It is possible to
produce a loss of capacity in both NiCd and NiMH by consistently
overcharging them but it has nothing to do with how far you discharge
them.

therefore can be 'topped up' or charged at any time without
affecting battery life.

So can NiCd with the right charger.

Is this the crux of the matter? Is the charger in some respects
as/more important than the batteries?

Absolutely. Broadly NiCd/NiMH chargers fall into one of three groups.
Firstly you have the ones which take a long time - at least 10 hours,
to charge a battery. These treat the battery well and won't harm a
battery if its only slightly discharged when you put it on them or if
you leave it a few hours too long. Charging at 10th of capacity
(C/10) is the safest way of charging but not terribly practical for
tools in use all day.

Secondly you have the ones supplied with cheap battery tools. These
usually charge in somewhere between 3 and 5 hours and have no charge
regulation worth talking about. These are damaging to batteries and
if left for more than a short time after charge is complete (as short
as an hour) will often significantly damage them. The poor battery
life on cheap tools is often a function of the poor chargers rather
than the batteries.

Finally you have the well controlled 1hr fast chargers which monitor
the battery state and modify the charging accordingly. Really good
charge control is essential for LiOn as overcharging turns them into
small explosive devices.

Basically if a battery is getting hot on charge it is being hurt.

So, to rephrase my question, could we have a section on batteries
(power tool) in the Wiki to make matters clear for the battery
numpty like me?

We could certainly produce a chart comparing the characteristics of
the various battery types. There isn't a single "best" one for all
purposes. If we did no more than warn against the damage the cheap
5hr chargers do to batteries it would be useful.

Thanks Peter, very helpful.


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk