Re: NiCad battery memory...
It is NOT a myth and CAN happen. In general terms here is how it works....A battery is a chemical storage device that contains an acid and metallic paste. The acid combines with the paste and through this chemical reaction electricity is released and a new chemical is formed. Charging the battery forces the acid and metallic compounds to seperate back into their native forms to be ready for discharging again.
If the NiCad battery is not fully discharged for many cycles, the uncombined metallic paste at the bottom begins to 'clump' its' crystals into larger units. In order for the battery to deliver current, the chemical reaction must take place quickly and this happens easily in the normally used portion of the battery because the material is in a very fine and reactive state. When the acid works its' way down to the 'clumps' the reaction slows greatly because the larger crystals take longer to dissolve. The battery voltage drops when this happens.
Fully discharging the battery on occasion makes ALL the chemicals combine and recombine and keeps the metallic compound in a fine and easily reactive state. Pretty simple, really. I encountered memory in a cordless drill owned by a friend that, when new, would drill many holes and had great durability. As it aged, the hole count went down and down until it could only drill a few before going dead.
I let it sit for 10 hrs and it would run at full speed again! But, it had NO torque and couldn't do any work. This was the memory effect. The crystalline structure was so coarse that it took a long time for the reaction to take place and limited the current available. That drill ran for about 20 minutes and then slowly died. Dead. I repeated this process twice a day for 5 days until the drill wouldn't run but a few turns after sitting the 10 hrs. Now, all the metallic contents had been dissolved into the acid and it was ready for recharge.
Full charge time later we had a VERY healthy drill battery again. Full capacity and great durability had been restored. This happens on lots of NiCad batteries that are repeatedly partially discharged and recharged. It takes lots of time and cycles for it to happen, but it can. The NiMh won't develop this phenomenon because the structure inside won't 'clump'...so to speak.
You certainly don't need to deep discharge your batteries every cycle. If I haven't used a battery for a time I discharge and recharge and then measure the charge with a recycler to make sure the battery is up to capacity. If it falls short, a second charge/discharge cycle should bring it up to snuff...if it is good. .