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Best practice for maintaining my NiCd Recharable Battery (18V 1.7Ah)?

Best practice for maintaining my NiCd Recharable Battery (18V 1.7Ah)?


Old 05-10-07, 02:04 PM
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Unhappy Best practice for maintaining my NiCd Recharable Battery (18V 1.7Ah)?

I have 4 related questions but before i get to them please read the details first:

I recently purchased the Worx 18V WG150 Grass Trimmer. This trimmer came with 2 recharable batteries (each battery is: 18v 1.7Ah NiCd). The trimmer included a battery charger with a feature to automatically prevent these batteries from overcharging (it monitors heat). The trimmer only uses 1 battery to operate.

My 4 questions:

1. Both batteries have not been charged yet (they are fresh out of the box). Because i want to only use 1 battery can i just pack the 2nd battery away in storage (completely discharged) for maybe a year (or more) and when i need it i can just dust it off, fully charge it, and get going?
Additional Details

2. To best maintain my battery, i was thinking i should FULLY charge it (from a completely discharged state) on the day i need it (charging takes 1 hour when battery is completely discharged), and then use the trimmer until the battery has been completely depleted (a complete cycle). And then store the battery, now entirely discharged, until i need it again maybe a month or more from that point. Is that an acceptable plan, realizing that the battery will be stored totally discharged for long periods?

3. If i fully charge it then how long can i keep the battery in this charged state before i must discharge it? Are there any consequences to keeping it fully charged for long periods besides a potential 10-20% self-discharge occurring? (i.e., will the battery become damaged?)

4. Is it best to keep the battery entirely discharged when storing it for long periods? How long can i keep it stored in a discharged state before i must fully charge it again, if necessary? Does the battery become damaged by being entirely discharged for long periods?

Thank you.
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Old 05-10-07, 02:15 PM
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Just use it, and everynow and then let it die completley .
Old 05-10-07, 02:30 PM
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What's the manual say? My Craftsman drill says not to let the battery completely discharge while using it. Ruined my old battery that way.
Old 05-10-07, 03:37 PM
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NiCd batteries are not suppose to completely discharge, as soon as you see the power starting to fade, it's time for a charge, discharging completely only damages the packs. I have about 8 dewalt 18v batteries that are 2 years old that I do this to. Still work like a charm.
Old 05-10-07, 04:56 PM
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The manual for this grass trimmer says absolutely nothing...i get the impression that they are more eager to make money off replacement batteries and thus say nothing on how to maintain it...replacement batteries cost $59.99 while unit itself costs $99 (with a battery included)...so most of cost of unit is the battery...reminds me of the printer market (making money off ink, not the printer sale).

So you guys think it is best to keep it fully charged as much as possible?
Old 05-10-07, 06:21 PM
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Seems like it was designed to be used more often. A frequency of only every few months seems more practical for a cheaper trimmer (more powerful to boot) and an extension cord, but it's your call.

But I second the vote NOT to discharge them completely. When the power starts to fade, the cycle is over.
Old 05-11-07, 12:35 PM
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No matter what you do, the battery will die eventually. If the battery is simply sitting on the shelf unused, it is still decaying at some rate. That is simply part of the cost of battery powered tools.

The first thing that you have to understand is that you need to distinguish between a NiCd _cell_, and a battery, which is composed of several cells. The rules applied to an individual cell change when you have a bunch of them electrically connected to form a battery.

The absolutely _worst_ thing that you can do to a cell is to 'reverse charge' it. Reverse charging is what happens when discharge current keeps flowing after the cell reaches zero volts. The cell starts to actually charge, but with reversed polarity. When you have a battery, one cell will always discharge first. The other cells keep powering the circuit, so the first cell to discharge will get 'reverse charged', likely damaging the cell. This is why you should _never_ deeply discharge a _battery_. You will almost certainly damage some of the cells in the battery.

When a battery sits in storage, the various cells undergo 'self discharge'. Since each cell is slightly different, you can be certain that after a long period of storage the cells will be in tremendously different states of charge, some pretty full and others essentially at zero. This sort of mixed up battery presents your biggest problem.

If you try to 'quick charge' such a battery, some of the cells will quickly reach full charge and then start overcharging. Other cells will still be on the way up, and will likely never reach full charge. If your charger is reasonable, then after a few charge/discharge cycles, the cells will have equalized.

Beyond this point I am just guessing:

My hunch is that if you _discharge_ the battery to a normal level (not to 0V, but just until you would normally say 'oh, I _must_ recharge now), and then store the battery, then the next season _all_ of the cells will have self discharged to 0V, but with no reverse charging. But this is just a guess, and if there is something actually drawing current from the cells (say a temperature monitor circuit), it might end up reversing some of the cells.

My personal procedure (read my personal mythology) for commissioning new NiCd and NiMH packs (or to re-commission them after storage) is to manually trickle charge them at C/30 for 35 hours. The C/30 charge rate is simply the mAH rating of the battery divided by 30. This is intended to charge and equalize all of the cells, but limiting overcharge to a rate that the battery can tolerate. The C/30 overcharging will 'cook' the cells slightly, but I figure that the reduction in life is worth the equalization.

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