would charging a cell phone or aa (nicd or nimh) intermittently decrease it's life?

[the judge]

i have a flashlight charger and i get about 4.5v @ 50ma and i want to know if i could use that to use it as a cell charger or aa charger when im watching tv or whatever, but if the life of a battery is based only on the number of cycles it goes through and if charging it a little, waiting then charging it some more until it's full would count as more that one cycle, then it probably wouldn't be worth it. i have 4.6v 25f supercap, so if i put it in parallel, would that help?

 

[MikeMl]

The thing that screws up NiCads is leaving it plugged into the charger too long, or recharging it before all the capacity is used. Best NiCad utilization is to have two battery packs. Use one until it is discharged, and then swap it. Charge the first one and dont swap again until the second is discharged. i.e. always use full-cycles; partial cycles are bad.

NiMhs are less fussy than NiCads, but aggressive charging after only a partial discharge will screw them up, too. Most appliances use a 0.3C or higher charge rate to recharge. Charge cycle end detection relies on measuring a temperature rise in the battery pack. If you only partially discharge, and then begin a new charge cycle, the charger doesn't know that the battery is full until it get hot. The battery life is determined by how many times you heat it; not how many times it got discharged. If you start to charge, and terminate the processes before the battery gets hot, then use up some of charge, and begin charging again, that would only count as one heating cycle.

 

[the judge]

can u determine when a nimh battery is full by checking the voltage? (i dont know how to check it by sensing heat) i had some trouble with this before when making a simple portable usb charger out of 4 nimh aa because most of the battery sets i tested got ~5.5-6.2v after charging from a supposed smart charger. i couldn't figure it out, but if it senses heat to stop charging, then that would explain things.

 

[MikeMl]

can u determine when a nimh battery is full by checking the voltage? ....

No, not reliably! That is why the battery packs used in, phones, drills, power tools, always have a thermistor built-in to the pack.