Dewalt 18v (2006) rated capacity 1200 mAh measured 10000 mah
Dewalt 18V (2007) 9096 rated capacity 2000 mAh measured 2100 mAh
Dewalt 18V (2010) 9096 rated capacity 2000 mAh measured 2200 mAh
Dewalt 18V (2010) 9096 rated capacity 2000 mAh measured 2200 mAh
Dewalt 12V (2006) rated capacity 1200 mAh measured 1100 mAh
Dewalt 12V (2006) rated capacity 1200 mAh measured 1100 mAh
Dewalt 12V (2008) rated capacity 1200 mAh measured 1200 mAh
Batteries are like cars take care of them and they will take care of you. I am not sure about the 9096 dewalts they could be using the 2100 mAh cells.
I do like the NICD batteries because it is a tried and tested chemistry for over a few decades. Unlike what most people believe, there is no scientific evidence that NICD batteries suffer from memory effect. The memory effect was observed on the first generation satellites that were orbiting the earth thus a battery got the same amount of charge paired with the same amount of discharge. That misinformation somehow made it here to earth, but rather than suffering from memory effect NICD batteries do suffer from voltage depression.
Voltage depression happens when a cell’s voltage is lower than the nominal voltage that a cell is rated at. The cell’s capacity does not diminish, but because of the voltage depression batteries do seem to be weak because they produce less overall voltage. Less voltage means that there is less electromagnetic force produced by the motor coils thus the user does experience that lazy effect.
Why do our batteries degrade over time?
The chargers that are supplied with most cordless tools are rapid chargers, they charge the battery at 1C (c = cell’s capacity.) meaning that in one hour the battery is charged and ready to go. In actuality a battery is roughly 80% charged, which is a subjective term as we’ll explore later. At this point the cells are reaching near the 90 – 95% charge state, as they are no longer able to accept more energy the voltage supplied to a cell drops called the delta peak. Your charger is programmed to recognize the delta peak voltage and shut off. After the initial bulk charge, there is usually a top off charge that charges the cells at a smaller current for a few hours until all cells are topped off at which point the charger switches to trickle charge mode where it supplies the smallest amount of current to offset self-discharge.
Over time as we use up our batteries, the cells which are connected in series do not all charge and discharge with the same exact rate. As a result cells become imbalanced, usually after 20 to 30 cycles. Now we charge those imbalanced cells and the first set of cells that reach their full charge potential signal by the delta peak to the charger that it is time to terminate charging. The charger does terminate but instead of a 90% charge when all cells were properly balanced, we may only have a 60% charge. The undercharged cells will never come up to full charge thus the user thinks that this is memory effect by noticing the battery’s diminished power output.
When we start to use the battery with imbalanced charged cells, the partially discharged cells are depleted first, giving us a false reading that the battery may be at its end not holding capacity. We may only have a cell or two that are undercharged, which leads us to further use the battery pack and deplete the fully charged cells. By doing so the cells that are undercharged and fully depleted first to 0V will reverse voltage (cell reversal) which over time causes permanent cell damage, although modern cells do tolerate cell reversal up to -0.4v to -0.6v without any adverse effects.
The rapid chargers that most tools are supplied with do not help either, with an imbalanced cell delta peak may come too late for come cells. If a battery has more undercharged cells then fresh cells, overcharged cells overheat, boil off any excess material off of the electrodes, and create crystals which all lead to premature cell failure. Once active material is boiled off a cell, permanent capacity loss occurs as there are fewer chemicals in contact with the electrode. Overcharging also creates crystals which increase cell’s internal resistance and puncture through separators that are designed to keep the various chemicals separate.
Most of us also do not use our tools for an extended amount of time, and over time as cells sit unused chemicals become stale, thus during the charging and discharging process they do not migrate as easily as they would on a battery that is frequently used.
The only proper way that I have experienced in balancing all cells in a battery is to charge it at 0.1C for 16 hours. This is a tried and tested method that safely brings all cells to a full and complete charge. Undercharged cells will be able to fully charge, while overcharged cells will be able to safely expel excess energy trough heat dissipation without any adverse consequences of having active material boiled off and crystal formation. Then discharge the pack at 0.2C until 0.9v/cell, which will allow you to measure the true capacity of the battery according to international standards and safely cycle the battery.
NICD batteries should be cycled when not in use for longer than 3 months to exercise the cells. 1 cycle is to charge 0.1C for 16h, rest for 1h to allow battery pact to cool off and discharge at 0.2c to 0.9v/cell. Store batteries discharged, contrary to popular belief discharged batteries cannot form the damaging crystals. Recharge the battery right before use, note all my batteries are discharged when in storage, I only charge them when I need them and there is no adverse effect in doing so.
Example: when I bought my dewalt 12v 2006 batteries, I could only get 700 mAh when charged at the 1c rate. After about 3 or 4 cycles that same battery pact was giving me 1100mAh. We can see that some irreversible damage was done by the previous owner, but this was a great deal from ebay and I was willing to accept the risk for the deal I got. To be fair the dewalt 2006 18v battery was in use most of its life without me knowing anything about NICD chemistry or the maintenance required, as you can see it has suffered the most capacity loss out of all the batteries.
When cycling a fully charged battery it is also recommended that right before recharging, discharge the battery to below 0.5v/cell. There is a study floating on the internet done by the Navy which states that cells that are cycled below the 0.5v/cell threshold once every 3 months further reduce the chances of any crystal build up. I have been practicing this on all my batteries without any adverse effects.
To sum it up:
1. Use your rapid charged for normal battery operation. Remember that the rapid charger is not that good with equalization although my Dewalt states that it does so, I have found through measurements that it is somewhat sufficient but not as good as a good quality RC charger.
2. Every 20 – 30 cycles or once every three months whichever comes first perform an equalization charge to restore and balance battery pack cells. Discharge to 0.9v/cell, very slowly discharge to below the 0.5v/cell threshold, charge at 0.1c for 16h and return the battery to service. If battery is being stored discharge to 0.9/cell.
3. I have found that a good RC charger will do a much better job at equalization as it can be pre-programmed with charge/discharge cycles, the set it and forget it mentality.
You can use the poor man’s method by watching a volt meter and using your tool’s charger for equalization, but I have found that with the RC charger everything is much more automated and less time consuming.
During normal use, if you are unable to wait for a battery pack to cool off, charge it upside down, place the battery on a flat surface with the charger suspended in the air. This ensures that heat escaping the charger does not heat the battery, and the battery by being in contact with a much cooler ground surface receives additional cooling while being charged.
With these steps, your NICD packs should last a long time, my 2007 and 2010 18V batteries are as fresh as when they were new.
Li Ion is a completely different beast, yes it will not have the self discharge of the NICD pack and yes it can be recharged more rapidly, but be careful about the lifespan of the Li Ion battery pack. Due to the very low internal resistance quality cells should be protected. Shorting a Li Ion cell can cause it to burst to flames, overcharging it will do the same. The constant current / constant voltage (CC/CV) is much cheaper to implement on these cells but if the charger is even slightly off by 0.1V battery degradation and permanent cell damage may occur.
Li Ion cells do not like to be discharged below the 3.700v mark, thus a user will be using his Li Ion battery pack and suddenly notice it run out of juice, instead of the steady degradation of power observed on the NICD/NIMH cells. This is due to the protection mechanism kicking in and protecting the battery from over discharging. Most chargers will terminate around the 4.200v mark, studies have shown that if a charger terminates at around 4.300v, by overcharging the battery by a mere 0.1v the cells lifespan will be shortened from the usual 500 cycles to as low as 100 – 200 cycles. Take that same cell and charge it to only 4.100v and you may increase the cell’s lifespan up to 1000 – 1500 cycles. Secondary all Li Ion batteries have a secondary lifespan which starts to tick the minute a battery is assembled. This is due to the chemicals eventually eating through the separators shorting a cell, one reason why no matter how easy or hard you use your cell phone, every 2 to 3 years the Li Ion battery has to be replaced.
The advantages of Li Ion batteries: their low self discharge, lighter battery pack, and ability to fully perform in sub freezing temperatures. This is a fairly new chemistry and hopefully through more R&D the pitfalls of this chemistry will be resolved.
One just has to make an informed decision on which chemistry is better, each has its advantages and disadvantages.