My string trimmer runs on a rechargeable NiCd battery. It's only two years old but doesn't hold much of a charge anymore. The trimmer manufacturer's tech support suggested that I may be able to bring it back to life by discharging the battery completely, charging it for six hours, and repeating this cycle three times, only charging it for one hour the final time. After each of the charges, when I attached a clamp to the trimmer's switch to let it run so it would discharge, it certainly did seem to have plenty of power. But after doing this process, when I went to actually use it, the trimmer barely had enough juice to spin even though I had left the battery on the charger for several days after doing the cycling process.
Does this technique of bringing a NiCd battery back to life work? Once I charge a NiCd, can I leave it in the charger until its next use or must I take it off the charger after a certain time? Do I have to discharge the battery completely before recharging it every time I use the trimmer?
Bob, thanks for that link. I checked it out but, with shipping, rebuilding my battery would run around $66 while a new one is $40. But it looks like a good resource for future battery needs.
When you have a multiple cell Ni-Cad pack as most battery packs are, you run the risk of reverse polarizing one of the cells. All the cells within the battery pack are not created equally and one cell will be discharged completely before the entire pack is exhausted. When this happens and you continue to discharge the battery pack the already discharged cell will be put under a reverse voltage charge and may be rendered useless.
It is best to only discharge Ni-Cad packs to 1 volt per cell.
In the late eighties, I had some really good drills, by Skil. Model 2230, if memory serves. Replacement set of batteries was about $28, and I got some new Black and Decker drills on sale at Home Depot for $20 each. The Skil got tossed out, then.
But you already know the $40 one is crap. So, your choice is to buy another crap battery or rebuild the one you have with higher quality larger capacity cells.
yeah sadly most products are designed lowest cost first.
worse the new battery pack was likely built as a spare when your device was manufactured, and has been sitting in a warehouse slowly going bad ever since.
They say to discharge NiCd batteries before recharging to avoid the "Memory Effect".
However, there are 2 effects of NiCd - "memory" and "voltage depression".
The latter is avoided with faster charge time "smart chargers" that detect "full charge". Overcharging a NiCd reduces its voltage by 4% or so, but that is often repaired by full recharge after full discharge.
The former is actually less of a problem, mainly cropping up if partial discharge to same extent as before followed by recharge is repeated to great extent.
Meanwhile, overdischarge of NiCd batteries appears to me to be the main cause of damage.
If you have NiCd batteries, I find best so far for a "maintenance proceedure" is to discharge them until they have voltage "in an earlier stage of going downhill" due to approach to full discharge, and then fully recharge them.
They should also be recharged if not having any recharging in the past year, maybe 6 months. I think more like 6 months for NiCd if recharged by a "smart charger".
Rechargeable batteries do not last forever no matter what you do. If you get them to be useful for 7 or 10 years, you are doing well.
One more thing - chargers with instructions to charge for 14 hours or anything more than 8 hours appear to me to be mostly "dumb chargers" that have a high rate of achieving significant overcharging. That "should cause at most minimal damage", though can cause the above "voltage depression" in NiCd and, if repeated frequently, can shorten life of NiCd and especially NiMH. If you want to guard against this, get a voltmeter connected to the battery pack while charging it - if it takes a rise from a stable level around 1.26-1.3 volts per cell to something higher and then stabilizes or "peaks out", then the battery has been fully charged and is being overcharged. Watch out for a series of alternating voltage stabilizations and rises as each cell in the battery achieves full charge at a different time - I find better to get all cells fully charged at expense of mildly overcharging some cells.
NiMH has no "true memory" and much less than NiCd of "voltage depression", but appears to me to be aged more by overcharging than NiCd is. However, damage from overcharging of NiMH appears to me to be small enough to be better worth charging a "series pack" until all cells are fully charged as opposed to charging until one cell achieves full charge.
I actually like "smart chargers" of kind that achieves small extent of overcharge due to delay of detection of full charge - by detecting directly (with a temperature sensor) or detecting indirectly (voltage peaking out and then decreasing, apparently-to-me as result of temperature rise) that results from overcharging. I like such "smart chargers" for actually minimizing overcharge in comparison to "dumb chargers". Such "smart chargers" tend to have charge time 4 hours or less.
Bottom line - it appears to me that if rechargeable batteries are "optimally babied", they last maybe 7-10 years and occaisionally more, and if "used reasonably well" they last 5-7 years.
I would not fret about minor to moderate deviation from "whatever is optimum treatment" for rechargeable batteries, since they will die and need to be replaced anyway - they will degrade at some rate or another no matter what you do! I think better to have them have a well-utilized good life and not fret too much! If you get both at least 4 years and 200 discharge-recharge cycles with a rechargeable battery 1/3 as good as new (in terms of time supplying "sufficient voltage" to the load, at least 1 or 1.1 volts per cell) afterwards, I think you are doing well!
Hi You can revive your NiCd battery in 5 minutes, simply google nicdfix, or visit
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they have a download able guide that will explain you how to fix your nicd battery. Thanks
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