Subject: Makita 9.6V Batteries

From: [email-masked] (Steve Swihart)
Date: Mon, 31 Mar 1997 21:45:25 GMT

Hello.

I have 3 9.6V Makita batteries.  One is 6 years old, 2 more are 5
years old.   Those babies never charge all the way any more and the
charge they take doesn't last very long.

I've heard rumors they can be "recycled" by draining them for a long
time across a resistor and charging them differently than the charger
does.  Is this true?

FWIW, I drain the battery until the drill won't turn at all before
charging.  Is this correct procedure?  I don't use them every day,
they're home tools.

TIA.

-Steve

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From: [email-masked]
Date: Mon, 31 Mar 1997 23:09:09 -0500

> time across a resistor and charging them differently than the charger
Probably not in your case.  Nicad batteries are designed for a finite
number of charge/discharge cycles (I believe typically 500) and yours
are most likely just at end of life.  Batteries used in a drill are
subject to a lot of heating when the drill is loaded heavily and that
accelerates the drying out of the chemicals in the battery.  Once that
happens, nothing you can do externally will help.

> charging.  Is this correct procedure?  I don't use them every day,
Sounds right to me.  I'd also let them cool down before recharging.  I
have the same Makita batteries (and maybe drill) and I'll be well
satisfied if mine last 5 years!

Chris

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From: Martin Eastburn <[email-masked]>
Date: 1 Apr 1997 06:20:44 GMT

Being an Air R.C. type also (sometimes) I deal with ni-cads
of several types.

What you have, (me too), is a battery that has several sets of 8 
batteries.  Each set is 8 cells, and each set is then attached + to +
for parallel capacity.  This helps us when one dies the pac doesn't -
just less power. 

If you discharge the set to 8V - 1V per cell in the series set of 8...

That is if you have a voltmeter - the voltage across the battery
is 8V or slightly less - this is optimum recharge level.
Sometimes Nicads (always) - retain memory - e.g. discharge down to the
level of last starting charge. - giving less and less power, but has
voltage.
If you have a friend that has RC cars or planes - perhaps they (M or F)
can help you with their nicad discharge capability. -

A resistor discharge with current limit, so excessive current isn't 
allowed.  You can do this if careful. Don't discharge below 8V across
the battery.

Your drill may not start to function due to lack of current, but the
battery has voltage (memory problem). 

so - yes if you are cautious resistor/autolamp can drain down the 
battery - but watch the voltage.  This will - repeat - will
erase 'memory', but NOT an OPEN CELL in a string of 8.

An Open is just bad luck.  
These series-parallel packs are generally great but tough to fix 
due to the container.
Martin

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From: "G. Vaughn" <[email-masked]>
Date: Tue, 01 Apr 1997 07:40:38 -0700

One of my three 9.6V Makita batteries displays similar behaviour.  This 
topic of NiCad "memory" was the subject of a long thread a couple of 
months ago.  Most replys seemed to support this.

I went to the Makita Service Center here in Denver a few months ago to 
get a replacement part for one of my tools and picked up a handout (copy 
>from  service manuals ?) which disputes this.  Makita claims that 
properly designed battery packs do not display this "Voltage 
Depression".  The handout is long and quite detailed, but some of the 
points that it contains are:

Do not condition a battery by deep discharge -- it could cause cell 
reversal (what ever that is).
Recharge a battery when there is a drop off in torgue, do not let it 
completly discharge.
Let the battery cool to room temperature before recharging, a warm 
battery will trigger the thermal cut-off switch, preventing a full 
charge.
Avoid recharging a battery that is full charged.

I have followed these guidelines and my battery packs seem to work well, 
but one (old one) still doesn't last long.  

Ken Vaughn

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From: damian drewek <[email-masked]>
Date: Tue, 01 Apr 1997 10:12:31 -0600

> charging.  Is this correct procedure?  I don't use them every day,

The recommended procedure has changed.  By draining all the way, you
tend to damage the weaker cells within the battery.  Those batteries you
have are pretty old and recylcling mayn not work.  I not sure of the
exact procedure, but I had someone try it on mine (same ones) and it did
not take.  New batteries work wonderfull.  Drill starts to slow down, I
then charge them right away.

Damian

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From: "Phil Anderson" <[email-masked]>
Date: 1 Apr 97 17:32:32 GMT

Steve,

I'm not an expert, but I think you are risking "polarity reversal" by
draining the batteries that far.  Safer, I think, is to run them until you
are not receiving the expected performance from your drill or whatever. 
Then, just charge them normally.  Another key point here is to be sure of
the ambient temperature in the charging area.  It should be something like
60 to 100 degrees, or thereabouts.

Good Luck

Phil
-- 
Located In The Woods of Beautiful Bonney Lake Washington

Steve Swihart <[email-masked]> wrote in article
<[email-masked]>...

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From: [email-masked] (Len Collins)
Date: Wed, 02 Apr 1997 01:34:44 GMT

Steve, Chris has given you accurate information except for running the
drill until it wont turn any more.  Each of your batteries is made up
of 8 individual cells of 1.2V each connected in series (the same
current passes thru each) and these cells are not matched in capacity.
When your drill starts to lose power this signifies that the cell with
the lowest capacity has run down.  If you continue to to use power at
this point the remaining cells will force current thru the depleted
cell in the discharge direction.  This is one of the two main causes
of damage to a NiCad battery, the other is heat.  If you could get to
the terminals of each cell and discharge them individually you could
run them completely down without damage.  But since they are in series
this is not possible.  I run my 12V unit only until there is no doubt
that the battery is discharged.  Then I usually wait till the next day
to recharge so there is no chance of overheating.  Since I have two
batteries, this allows me to continue using the tool.

There is some mis-information about the memory that can be exhibited
by NiCad batteries when they are discharged to exactly the same point
repeatedly.  This memory is difficult to demonstrate because the
cutoff point must be very precise and requires accurate laboratory
instruments to reproduce.  The loss of capacity generaly attributed to
memory is actually a voltage depression caused by overcharging.  There
are few chargers that are capable of properly charging a NiCad.
During charging, a battery will exhibit a slight dip in voltage just
after full charge is reached.  Some of the more expensive chargers
(for model cars and planes) will sense this dip in voltage and shut
off at this point.  But these units generaly cost more than your
drill, charger and battery.

Heat in a battery can be caused by charging or discharging at a high
rate.  If this heat is excessive it will cause the internal gasses to
escape through a vent provided for this purpose, without this the
battery would explode if it had sufficient heat.  I have overcharged
batteries until they boil and bubble liquid out this vent.  After
venting the capacity will be reduced.

A NiCad battery may be trickle charged indefinately as long as the
charging current does not exceed 1/10th the rating of the battery.
For example, an 1800mAh battery could be left on a trickle charge of
180 mA.  However, about 80% of that value would be sufficient to keep
the battery in top charge condition and ready to go with full
capacity.  The problem with the chargers that automatically switch to
trickle is that if the power goes off they come back on at full charge
and the battery is already charged.  Without the trickle charge the
battery will lose most of its charge in a few months.  So most people
stick them back in the timed charger and overcharge them again.

I agree with Chris, your batteries have served you well, time for new
ones.  Hope this helps you to understand what to watch for with your
cordless tools.

Len Collins
Retired Electrical Engineer
Now flying electric model planes
and malforming wood
--------------------------------------

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From: [email-masked]
Date: Wed, 02 Apr 1997 09:39:53 -0500

Len Collins wrote:
> this is not possible.  

That's good advice Len, and absolutely true for most NiCad operated
equipment.  In the case of the Makita drill however, the electronic
control circuit that actually runs the drill motor "drops out" before
any of the cells are completely exhausted.  It's a good design and
probably explains why Steve's batteries have lasted as long as they have
without experiencing a cell reversal failure.

Chris Hubner