Discontinue the use of chargers that cook batteries.
After the initial fast charge, some fast-chargers apply a timed topping charged. In an attempt to gain a few extra capacity points, some chargers apply a measured amount of overcharge. The capacity gain is about 6%. The negative is shorter cycle life.IBM ThinkPad T60 Battery The recommended trickle charge for nickel-cadmium is between 0.05C and 0.1C. Because of memory concerns and compatibility with nickel-metal-hydride, the trickle charge is set as low as possible.
Charging nickel-metal-hydride
Nickel-metal-hydride chargers require more complex electronics than nickel-cadmium systems. IBM 40Y6799 Battery, IBM FRU 92P1139 Battery, IBM FRU 92P1141 Battery, IBM FRU 92P1137 Battery,To begin with, nickel-metal-hydride produces a very small voltage drop at full charge and the NDV is almost non-existent at charge rates below 0.5C and elevated temperatures. Aging and degenerating cell match diminish the already minute voltage delta further. This makes full charge detection difficult.
A nickel-metal-hydride charger must respond to a voltage drop of 8-16mV per cell. Making the charger too sensitive may terminate the fast charge halfway through the charge due to voltage fluctuations and electrical noise. Most of today's nickel-metal-hydride chargers use a combination of NDV, rate-of-temperature-increase (dT/dt), temperature sensing and timeout timers. The charger utilizes whatever comes first to terminate the fast-charge.
Nickel-metal-hydride should be rapid charged rather than slow charged. Because of poor overcharge absorption, the trickle charge must be lower than that of nickel-cadmium and is usually around 0.05C. This explains why the original nickel-cadmium charger cannot be used nickel-metal-hydride.
It is difficult, if not impossible, to slow-charge a nickel-metal-hydride. At a C?rate of 0.1-0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full charge state accurately and the charger must rely on a timer. Harmful overcharge can occur if a partially or fully charged battery is charged with a fixed timer. IBM 40Y6799 Battery The same occurs if the battery has aged and can only hold 50 instead of 100% charge. Overcharge could occur even though the battery feels cool to the touch.
Lower-priced chargers may not apply a fully saturated charge. Some will indicate full-charge immediately after a voltage or temperature peak is reached. These chargers are commonly sold on the merit of short charge time and moderate price.
Simple Guidelines:
Avoid high temperature during charging. Discontinue the use of chargers that cook batteries.
A charger for nickel-metal-hydride can also accommodate nickel-cadmium, but not the other way around.IBM 40Y6799 Battery, IBM FRU 92P1139 Battery, IBM FRU 92P1141 Battery, IBM FRU 92P1137 Battery, A charger designed for nickel-cadmium would overcharge the nickel-metal-hydride battery.
nickel-based batteries prefer fast-charge. Lingering slow charges cause crystalline formation (memory).
nickel- and lithium-based batteries require different charge algorithms. The two chemistries can normally not be interchanged in the same charger.
If not used immediately, remove the battery from the charger and apply a topping-charge before use. IBM FRU 92P1137 Battery Do not leave nickel-based battery in the charger for more than a few days, even if on trickle charge.
A well-designed charger is a reasonably complex device. Taking short cuts will cost the user in the long run. Choosing a well-engineered charger will return the investment in longer lasting and better performing batteries.