Charging cordless phones?

So my family just got some new Panasonic 2.4 GHz cordless phones and as soon as we got them home I put the batteries in them. The phones displayed that the batteries were low, so I put the handsets on the bases to charge. My father diligently consulted the instruction manuel which said to charge them for 6 hours prior to use. My question is this: the batteries are Ni-Mh which I though had no memory affect. Will taking them off the charger prematurely actually damage them as Panasonic infers it might?

Thanks,
Brad

I honestly have no idea but when I buy a new cordless phone, I always charge it overnight.

Lisa

I'm not sure if the "memory effect" is the same as the initial charge.

I think it's mostly because they trickle charge, and they want to be sure you get ample charge the first time. Also, sometimes even with NiMh and LiIon cells you have to charge them all the way up, and then kill them the first time -- not for the sake of the battery chemistry, but to help calibrate the computer that handles the charging.

I tend to believe that there are only so many charging cycles in the average rechargeable battery. So, if you recharge it 200x from 95% to 100% full or recharge it from 10% to 100% full, you will only get 200 recharging cycles before it dies.

So... I tend to leave my cordless phones off of the charger for a week or two (until they show 1/2 or 2/3 discharge), then recharge them. The batteries seem to usually last a long time (several years or more) vs the 12 months +/- that leaving on the cradle would seem to give me.

Also, whether cordless or cell phone (or any rechargeable battery), I try to fully recharge it in one sitting vs a series of partial recharges.

There are so many different phones and charging circuits out there that it is probably hard to know which one is a smart charger vs just a 1/10c or 1/5c rate charger from model to model or mfg. to mfg.

I started doing this when I noticed on one old phone that the battery stayed warm all of the time--possibly indicating a fairly high "trickle" charge current--that was prematurely killing my battery.

-Bill

Thanks for the responses. Saaby, I had never considered that - that charging the battery fully could calibrate the charging circuit; very interesting.

-Brad

The impact of charging and discahargiung depend on the battery and the charger. The NiMH do not have a memory effect, but do have a limited life (in years) as well as limited charge cycles. The NiMH and Li-Ion are good for about 400 - 500 charge cycles.

The NiMH and Li-Ion are full discharge, so it will last a lot longer than expected if you only discharge it 10% every day and recharge immediately. That's what's making them work in hybrid cars.

A typical NiMH will discharge by 1% per day, and that accounts for the "initial charge" requirement. By the time you buy the phone the battery can be in just about any state of charge. The "initial charge" recommendation keeps people from calling tech support or returning the product when they only experience 10 or 20 minutes of talk time the first time it's used.

Leaving the phone off the charger till it needs a charge is a good idea for Ni-cad batteries. That takes care of the memory problem AND the charge cycle problem. Leaving the NiMH on the charging cradle is fine, assuming a decent battery charging circuit.

Daniel

Just remember that the NiCd "memory effect" or voltage depression has two causes...

The first that everyone assumes is memory effect is from partial discharging a battery. This was based on NASA's findings that NiCd batteries used EXACTLY to the same level of discharge time after time (i.e., crossing into and out of sun light on orbit after orbit) would reform the grain structure (that naturally forms in the "never discharged" region over time and temperature) where the battery would be unable to supply full voltage beyond the "memory" discharge level. No person would be able to reproduce this effect in day to day normal use.

The second type of voltage depression results from continual trickle charging which causes a conversion to a different form of crystalline structure, which can also somewhat depress voltage output.

The last which really kills rechargeable batteries is discharging a stack of batteries to such a level where you get one or more cells reversing polarity in the stack. This is the most likely will kill a pack quickly. Overcharging at a high rate can too.

NiCd Battery FAQ V1.00

<ul type="square">Summary

[*]DON'T deliberately discharge the batteries to avoid memory
[*]DO let the cells discharge to 1.0V/cell on occasion through normal use.
[*]DON'T leave the cells on trickle charge for long times, unless voltage depression can be tolerated.
[*]DO protect the cells from high temperature both in charging and storage.
[*]DON'T overcharge the cells. Use a good charging technique.
[*] DO choose cells wisely. Sponge/foam plates will not tolerate high charge/discharge currents as well as sintered plate. [/list]

-Bill

The only reason they say to charge for a certain minimum time is because most of the calls to their customer service number are due to a customer trying to use the product right out of the box with a low or dead battery. Following those instructions ensures that you have enough juice in the phone for normal operation for a reasonable amount of talk time. But the phone will usually operate normally with less charging than that. There will be absolutely no problem using the phone before the noted timeframe.

My personal experience with years of rechargeables is basically to charge them fully the first time and once in a while run them way down. You don't need to always put them on the charger when not in use. You don't have to run them dead every time. You should let the batteries fully charge the first time.

Ni-Cads, NiMHs, and even Li-ions are much improved over the past few years. Just avoid extremes in use and environment. As always, try to buy the best you can afford.

Mine in the phones last at least twice as long in use as the manuals say they should.

The two most recent Panasonic phones we purchased specifically said "safe to leave on charge" and are NimH packs.

I always tryed to get others to leave cordless phones off the charger, but was never succesfull.

BTW... the Panasonic phones ROCK!

I have been getting the Panosonic "Splash Proof" phones the last couple of times (including parents on both sides). Work great so far as none of the phones have had one hickup (only problem is the base station speaker phone on the older types has become useless with time on one unit).

-Bill

Thank you for your responses. I too am really liking these Panasonic phones; excellent build and sound quality and very ergonomic.

-Brad