Why does a matchbook sized cell phone battery require 3 hours to charge

most cell chargers are designed for trickle charging to avoid heat buildup or to charge off the power provided by the USB bus of a computer

Power tools arent as picky about contact with skin or heating the cells up (my hitachi lithium has a fan on the charger)

I think part of the theory is to charge the cell while its user sleeps or it otherwise stationary whereas if youre charging a tool battery its genrally to use it

I suspect the ability to dissipate the heat generated by the charging current is the difference. Another difference is the chemistry in the two batteries. Your DeWalt is probably nicad while the cell phone is NMH, or perhaps some more exotic chemistry.

Paul

Get a DeWalt cell phone!

If your cell phone is so mission critical that it must always have a fully charged battery you should have a spare battery and charger. I get all my cell accessories from:

're cheap and fast.

Your cell fone's battery is probably lithium-ion and it has strict charging requirements that are usually computer controlled. Your cell fone probably is the computer that is controlling its needs.

b

Bob, thanks. Based on some other responses, I am beginning to see what the issues are. That website seems to be well stocked, and I will buy a couple of things from them.

i

For the most part the faster you recharge a battery the shorter its life span. Three hours isn't all that bad though for a decent charge. They are probably trying to balance re-charge time with warranty expiration date.

Their (Motorola) old two-way radio equipment from a few years ago use to take 12-16 hours with a "standard" charger. Go talk to any of your local police agencies and ask them about radio/phone batteries, cost, charging times, life expectancy... you'll surely get an earful that you won't soon forget :)

I haven't bothered to look into the numerous consumer alert-type stories that have been on the TV news, but there have been quite a few regarding laptop and cell phone batteries starting fires, sometimes in pockets, briefcases or luggage.

It's been suggested/discussed here in RCM before, that in general, the best battery charging is slow charging.. both in terms of quality/level of battery output and long battery life.

The instant gratification or demand for instantaneous results (commercial uses) of power tool, or critical use batteries have contributed to the availability of rapid-charging battery chemistry and construction design technology.

Forcing rapid chemical changes can't be good for long battery life, and probably reduces the useful charge output, in most cases (for most types of batteries).

WB ......... metalworking projects

The minimum time to recharge a battery is restricted by the charge rate it can accept.

Graham

Your DeWalt battery gets very hot doesn't it. It is out in the air. The smaller battery that is inside a cover that might heat sink and might be even a heat source... Trickle current to slowly charge.

One hint - 120v chargers put out 10% more than operating current. Turn off cell phone and then plug it in. Faster charge.

Get a car unit - plug into the 12V socket - charges faster in any mode. Higher current available.

I keep the car one in the car at all times. I can get it if I need it for use on the tractor or generator (power out).

We charge at night - off and charge. Seems to work for us.

I think the real trick for you is turning off the cell.

Martin

Mart> My Motorola cell phone has a matchbook sized cell phone battery. If it

Only 10% more ? You have to be joking.

Graham

In my experience, at a 3-4 hour rate, the cells only noticeably warm up from getting fully charged and beginning to be overcharged. It appears to me that most "smart chargers" detect full charge by detecting directly or indirectly this temperature rise. What I suspect is an indirect detection of temperature rise is cell voltage decreasing after peaking from full charge. I suspect this is why "smart chargers" tend to work with shorter charging times of 4 hours or less.

Meanwhile, there are some aggressive chargers out there, such as 30 and

15 minute chargers for AA NiMH cells. 15 minute chargers require compatible cells of especially low resistance. I have a charger that actually charges 2,000 mAH AA cells in 15-18 minutes. It has a fan. The cells get fairly warm during charging, and are almost too hot to hold when they reach full charge.

- Don Klipstein ( snipped-for-privacy@misty.com)

I had a rechargable battery explode in my hand. It unwound like a biscuit can, and startled me. Hot batteries apparently have a bit of pressure in them.

Most of the battery folks I deal with recommend a charge rate of 1/10 the amp-hour capacity of the battery unless the battery is made specifically for fast charging. Fast recharge batteries get really warm toward the end of the charging cycle too.

The new lithium-iron phosphate chemistry looks promising since it can handle the high discharge rates and has very good recharge rate, capacity and cycle rating. (one-third to one-fourth size for a given amp-hour capacity and recharge time of 1-1/2 to 2 hours for wheelchair service and ~5000 charge cycles, for example)

Ya wanna see a lithium battery get hot? Short one. Wear safety equipment.:)

Cellphone batteries *are* designed for faster than 10 hour recharge though.

That's not what the previous poster said anyway.

Graham

Most cell phones I've owned lately, have had optional "travel- chargers" available from the manufacturer, which charges the battery in about 1 hour. Also the phone controls the charging so that when the battery is fully charged, it will stop charging. So, I don't think that the long charge times are unavoidable due to the battery type itself. There has to be another explanation... maybe it's a marketing thing... include the "slow" charger with the phone and sell the faster one as an "option" for about $40 more.

Martin sez:

"> I think the real trick for you is turning off the cell".

Right on Martin. It would be a real trick, and one he is incapable of. Iggy won't turn off any appliance he can bleat incessantly over and make a general nuisance out of himself.

Bob Swinney