Power Tool Batteries And Battery Memory Effect
Smart chargers can prolong the life of power tool batteries.
Today, the only problem with memory in power tool battery is in our own heads. Yes, we remember when power tools had memory problems but we just don't want to remember that someone told us that power tools have no more memory. Can you remember that?
The fact is that NiCad batteries like makita 1201 battery do have charging/discharging characteristics that we call memory but, in today?s batteries, memory is only important in sensitive electronic instruments that are affected seriously by very small variations in voltage. Power tools don?t react to those small variations and keep on running far beyond what a computer or cell phone would see as a voltage problem.
Locking off the trigger long after the tool has quit turning in an effort to ?drain down the battery? moves a battery into what is called Deep Discharge, a state that actually does chemical harm to the battery.
Pulling a battery out of the old fashioned chargers (which I still have several of in my shop) when it has stopped, and popping it right back in to get some ?extra energy,? moves a battery into what is called Overcharge, which can also do harm to the battery.
This article was supposed to be a comparison of the batteries offered by each manufacturer. What I discovered was that although the batteries have certainly improved over the last few years, what has really been a revolution in battery-operated power tools has been the evolution of the charging mechanisms, and this is changing so fast that a comparison today would be out of date before you received the magazine. So, let?s see if we can get enough of a handle on the technology to help to choose your next power tool.
Today?s battery chargers are actually mini-computers that are constantly testing the batteries and changing the charging strategy millisecond by millisecond to maximize the performance of the battery pack. Each manufacturer is using its own strategy, many of them holding patents on their particular technology. In reality, the NiCad batteries themselves are mostly quite similar: it is the chargers that make the real difference. I will talk about Nickel-Metal Hydride batteries in a minute.
First, batteries like room temperature. Trying to charge them when it is too cold or too hot either will not work well or will cause harm to the battery. Some chargers refuse to operate until the battery comes into the right temperature range. Moral: don?t try to charge batteries in hot sunlight, nor on a frozen construction site.
Batteries should not be over-charged, so most chargers today test the battery to see how much charge it needs, if any. If you stick in a full or almost full battery, the charging regime is adjusted accordingly.
Battery packs are made up of individual cells, of 1.2 volts each. But not all cells are created equal. Some are stronger than others and the battery pack can be limited by the weakest cell in the pack. Most chargers give a main quick charge to all the cells, and then move into various special charging techniques to equalize out the unequal cells. This process tends to rejuvenate the battery pack as a whole.
NiCad batteries lose from 1 to 3 per cent of their charge per day by just sitting around, so the final charging is often a trickle to avoid standby discharge. Of note, they lose power faster in higher temperatures, so a battery in a hot truck in the summer can lose half its power over the weekend.
Now, each manufacturer deals with all of these things differently in its respective chargers, some measuring cell temperature, others measuring cell voltage, some even testing discharge. All of them are using little CPU computer chips to create their smart chargers. In fact most of the smart chargers will accept many of the batteries from the same manufacturer, eliminating the need for a different charger for each battery type,such as ryobi replacement battery.
The FAST CHARGE concept is basically how rapidly they finish their initial rough charging ? ranging now
from one hour all the way down to Walter?s 15-minute Pit-Stop. But all of them require more time than their minimum ?fast charge? to really ?recondition? the battery pack and all of its cells.