What are the advantages of lithium ion batteries compared to other rechargeable batteries?
Lithium-ion batteries have several advantages:
They have a higher energy density than most other types of rechargeable cells. This means that for their size or weight they can store more energy than other rechargeable batteries.
They also operate at higher voltages than other rechargeables, typically about 3.7 volts for lithium-ion vs. 1.2 volts for NiMH or NiCad. This means a single cell can often be used rather than multiple NiMH or Ni-Cd cells.
Lithium-ion batteries have a lower self discharge rate than other types of rechargeable batteries. This means that once they are charged they will retain their charge for a longer time than other types of rechargeable batteries. NiMH and Ni-Cd batteries can lose anywhere from 1-5% of their charge per day, (depending on the storage temperature). Lithium-ion batteries will retain most of their charge even after months of storage.
So in summary; lithium-ion batteries can be smaller and lighter, have a higher voltage and hold a charge much longer than other types of batteries.
What are the disadvantages of Lithium Ion batteries compared with other rechargeable batteries?
Lithium-ion batteries are more expensive than similar capacity NiMH or Ni-Cd batteries. Lithium ion batteries are difficult to obtain in standard cells sizes (AA, C and D) like NiMH and NiCad batteries. Lithium-ion batteries also require sophisticated chargers that will carefully monitor the charge process. And because of their different shapes and sizes each type of Li-ion battery requires a charger designed to accommodate it's particular size. This means lithium ion battery chargers are more expensive and more difficult to find than NiMH and NiCad battery chargers.
Are the Lithium Ion cells dangerous?
Yes, all lithium cells are dangerous but Lithium Ion cells are inherently safer than Lithium Polymer cells because of their differing chemical makeup and steel case. Our Lithium Ion cells have a safety disc that ruptures to release pressure to avoid explosion. Follow the Lithium Safety Guidelines
in the Q&A.
I was making my own Ion Pro 2S Pack and accidentally touched the wires together and the batteries and wires got very hot. What happened? And are my batteries OK?
You probably shorted the positive and negative ends together which creates a completed circuit and the energy must be dissipated. In this situation, it will dissipate in the form of heat. If this happened for only a second or two, the cells should be fine. But leaving them in a shorted condition for an extended period can ruin them. You should be careful when handling the cells as a shorted pack will generate enough heat to burn your fingers.
I heard that if you run them below 3 volts per cell they are ruined. Is this true?
It is true that you should not run the cells below 3 volts each. However, in this application it is not a problem if you pay attention, because the car begins to slow long before they reach this point. It will be very obvious that it is time for a recharge. As long as you don't discharge the battery below 3 volts per cell you won't have any problems. Below 2.9v/cell, the batteries will need to be trickle charged around 50 mAh until they reach 3 volts per cell. Discharge below 2.3 volts per cell can do permanent damage. So when the car slows down, stop and recharge after letting the batteries cool! If you keep running, there is the potential to damage the cells. We have cells we have been running hard for months now with no problems as do many of our customers, but you do have to pay attention to this issue.
OK, I didn't bother to read the Q&A before and have ruined my cells, now what?
This is not a product defect, so you will need to purchase another set. Think of it like the guys who drag race and push their engines too hard and blow them up (hope that helps ease the pain).
Do Lithium cells have memory?
None at all. What determines the life is the number of discharge/charge cycles.
How long will these batteries last?
Lithium-based batteries have a lifetime of 2-3 years. The clock starts ticking as soon as the battery comes off the manufacturing line. The capacity loss manifests itself in increased internal resistance caused by oxidation. Eventually, the cell resistance will reach a point where the pack can no longer deliver the stored energy; although the battery may still contain ample charge. Increasing internal resistance is common to cobalt-based lithium-ion. The speed by which lithium-ion ages is governed by storage temperature and state-of-charge. Figure 1 illustrates the capacity loss as a function of these two parameters.
What is the best way to store Lithium Ion batteries?
Lithium-ion batteries can hold a charge for many months. If possible, store the battery in a cool place at about a 50% state-of-charge. The most harmful combination is full charge at high temperature. This is the case when placing the cells in a hot car. If a lithium-ion battery with a very low charge is stored for a long period of time (many months), it is possible for the voltage slowly drops below the level at which it can be charged again. If the battery is going to be stored for several months it's a good idea to take it out and recharge it after a few months. Better yet would be to actually use the battery every few months and then leave it partially or fully charged.
On the page about the Lithium cells it says they are 8.4 volts together but it says the individual cells are rated 3.7 volts each. Isn't that 7.4 volts and not 8.4 volts?
The cells come off the charger at 8.4 volts and drain down to 6 volts with 7.4 being the nominal (according to plan or design) voltage. The 8.4 volts is significant because this is the maximum voltage that a stock XMOD or MiniZ can handle.
Why are Lithium cells more expensive than other battery types?
Mainly because they are much more complex to manufacture and are manufactured in much smaller quantities than NiMH or NiCad batteries. But they are worth it for the performance difference. Something to consider is this, the Lithium cells are the future of the Remote Control hobby and the support equipment you buy such as chargers and other equipment should be considered an investment. Even if you tire of RC cars, Lithium technology will benefit your future hobby endeavors.
Can I solder directly to Lithium Ion cells? In other words, can I solder to cells without tabs?
No you cannot. The extreme heat (we solder at 660 degrees) will disrupt the cell chemistry and permanently damage them. They may still work, but the output will be greatly reduced. If you are going to make your own Ion Pro 2S Pack, you must buy tabbed cells. We have seen many kits sold on eBay and other sites that were direct soldered. These will have greatly reduced capacity.
How many times can you charge a Lithium Ion battery?
Our Lithium Ion cells are rated for 500 discharge/charge cycles, whether its a half cycle or full doesn't matter. This rating goes out the window if the cells are abused.