[Watchdog]

I'm aware that overcharging batteries is bad for them, but how is undercharging bad for them?

By shorter life, do you simply mean you don't get as much use before the next recharge, or does undercharging affect how many times the batteries can be recharged?

 

[Eagle_Driver]

Well, undercharging can also reduce the number of times that the battery can be recharged, as well, due to the excessive gases that can build up inside the cells.

 

[Pepzhez]

I have a Radio Shack rapid charger that I bought two years ago. I've noticed that it doesn't make any difference whether one leaves the charger plugged in long after the light goes off, or if you remove the batteries as soon as the charge cycle reaches completion.

One question I have is how many charges should one reasonably expect from a Ni-MH battery anyway? What is the longest useful life anyone has ever gotten out of one of these?

 

[Eagle_Driver]

I was wrong about how undercharging can damage batteries. If you keep undercharging the batteries, the batteries will permanently lose their ability to accept a full charge. In the worst cases, undercharging a 1600mAh NiMH battery will ultimately reduce its maximum capacity to as little as 1000mAh.

And contrary to popular belief, slow-charging nickel-based rechargeable batteries (especially NiMH batteries) can actually cause more harmful damage to the cells than proper rapid-charging! That's because the batteries can actually be overcharging even though the cells feel cold to the touch - and NiMH batteries have almost no tolerance whatsoever for overcharging. What's more, slow-chargers have no charge termination other than a simple timer.

The best type of charger, IMHO, is one that fast-charges batteries in three hours or less, and provide sophisticated means of charge termination ("smart" chargers), and use independent charging circuits for each cell (so you can charge batteries individually). Such chargers don't come cheap, unfortunately - expect to pay at least $40, and usually much more $$$, for a small 4-cell AA/AAA travel charger that provides those very features. Fully charged in such an expensive charger, NiCd batteries will usually last through 1000 to 1500 full charge/discharge cycles, while NiMH batteries should last about 500 cycles.

 

[PodMan]

why is it not good to store a battery fully depleted? this player i bought used came with a fully depleted battery. i notice playtime is no where near the advertised hours so I think i might need a fresh battery.

is there a good place online to buy new gumstick batteries?

 

[Eagle_Driver]

PodMan, NiMH (nickel metal hydride) rechargeable batteries should NOT be stored fully depleted, since that will permanently destroy the batteries' ability to accept a full charge. Storing them fully charged is okay, but for long-term storage, they should be discharged about 60 percent of the way, leaving about 40 percent of the charge still remaining in the batteries.