I've played a lot with batteries and model airplanes with all chemistries.... Lithium revolutionized our competition ready to fly R/C 10 ounce freestyle aerobatic models. I’ll have to stir the pot and try and recall all the stuff we learned over the years. I’m sure it will come back to me as write my thoughts below.
All of the aforementioned chemistries will work fine, some are better suited to form fitting and lighter weight but lack punch and staying power and are simply volatile while others are heavy yet durable don’t need much attention and provide stable discharge curves and are cheap too!. Energy density is paramount for model airplanes, trains don’t really care heavy or dense cells are the most robust… Some of the KEY factors in cell chemistry choices are energy density, charge retention, memory, charge/discharge cycle life and the more obvious discharge or performance curves. While not all the “best” aspects of specific chemistries are paramount for a given hobby some are definitely more suited than others for given applications.
NiCd’s are well suited; lowest internal resistance, durable, cheap, flat discharge curve, long life, NiCd doesn’t require fancy chargers and are safe….
NiMh’s are much like NiCd’s, however energy density is better, more expensive per Ah of capacity, less tolerant to abuse, requires more sophisticated chargers, forming or training is paramount (C/10 @ 20-24hours with at least three full charge/discharge cycles), Ni-MH capacity falls off with cycling (USE) whereas Ni-Cd stays pretty constant, seldom going below 80% before shorts develop. Ni-MH has a higher self-discharge rate (3-4%/day) than Ni-Cd (1%/day).
Lithium most expensive per Ah of capacity, energy density is (5) times that of other chemistries, fragile by some standards, form fitting is great, very sophisticated chargers required, volatile (thermal runaway) if charged incorrectly or with the wrong charger, less than half the cycle life others, don’t like to be subjected to or perform well under high discharge demands yet they have the best self discharge curves of all noted thus far.
Every chemistry has its specific quirks and requires its own specific type of charge regimen, all require maintenance some more than others. When Lithium was first brought to RC world we experienced multiple user miss-haps resulting in spontaneous combustion due to user interaction with miss-information, wrong charger type/charge parameters and expectations.
The best results for any chemistry is typically realized with lower charges rates. All of the chemistries listed above less PB/Gel/Lead must be used in multiple cell configurations or are stacked in series and or series-parallel to achieve ampacity/voltage numbers as required/desired. Periodic extended slow charge rates at C/10 hour rate allow the cells to percolate so to speak allowing all cells to balance themselves. Pretty much across the board cells are charged once they reach peak voltage respectively (in pack configurations ill balanced cells provide false peaks), fast charging does NOT realize good results in this consideration. Remember a battery pack is only as good as the weakest cell accordingly cells that have been graded are the best choice for pack building (maybe not really a factor in our hobby though).
“slow charge” The industry standard is any charge rate that will charge the cells in 10 hours or less.
"fast charge" The industry standard is any charge rate that will charge the cells in 1 hour or less.
This term "C" is numerically equivalent to the rated capacity of a cell. A cell discharged at the "C" rate will expend its minimum capacity in one hour.
At .25C discharge rate, a cell's one hour rated capacity will be delivered in four hours, and at the 4C discharge rate, the rated capacity will be delivered in 15 minutes. For example, the "C" rate of a 2400 mAh cell is 2400 mA. The .1C discharge or charge rate for this cell would be 240 mA or .24A.
Dollar for dollar, long term use and user interaction you simply cannot beat NiCd’s IMO… I don’t have much experience with PB/Gel/Lead cells perhaps they are a very good consideration if weight and size are not a factor such as a battery box car or the like.
It’s entirely plausible I made some mistakes in my comments above, It’s been a while…
Regards,
Michael
