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Author Topic: HT battery charging  (Read 2918 times)

Posts: 46

« on: July 13, 2012, 09:04:08 PM »

If you have a HT battery that is 9.6 volts and 700MAH and your wall wart is 12 volts at 200MA. Will it take about 3 and a half hours to get a full charge? Thanks Billy

Posts: 17484

« Reply #1 on: July 13, 2012, 09:48:02 PM »

It depends on your charging circuit and the battery.

You usually need to put more net power into a battery than the rated capacity.
With Ni-Cad batteries the recommended charging rate was 0.1 times the amp-hour
capacity for 14 hours, even though simple math might show it should only be
charged in 10 hours.

Optimum charging rates vary with different battery types.  Some are capable of
"fast charging", and can be charged in an hour.  Others need to be left overnight.
And the charge rate isn't constant:  it might take as long to get the first 80% of
the charge as it does to add the last 20%, often because more care has to be
taken near the end to prevent overcharging.

Chargers are actually pretty complicated devices these days in order to get
maximum life out of the batteries.  I have a charger that draws about 700mA,
and if I use a wall-wart that is rated at 500mA then it doesn't charge at all
because the voltage drops too much.  But connecting it to a 10A power
supply instead of the 700mA wall wart doesn't increase the rate at which
the batteries are charged.

So, back to your question.  If the battery capacity is 700mAh and the charger
can provide 200mA, you can't fully charge a dead battery in less than 3.5 hours.
Probably 4 hours is more like it.  But just because the wall wart is rated at 200mA
doesn't mean that's the charging  current into the battery.

When in doubt, read the manual.

Posts: 2409

« Reply #2 on: July 13, 2012, 10:13:43 PM »

You do not connect the battery to the 12V. There has to be some kind of circuit to control the current and voltage going to the battery. These days there are NiMH and LithiumIon batteries in use. They require a certain scheme to really load them well. There can be found a wealth of information at
All modern batteries are capable of rapid charging, so for a rough calculation you may say charging a 700mAh battery at 200 mA takes about 4 hours. Don't forget, your charging circuit will also consume a bit of the current. However, rapid charging is not good for the service life of batteries, see
There you can see that you may be reducing the life of your battery by 50%. Patience pays  Wink

Posts: 6252

« Reply #3 on: July 14, 2012, 07:57:21 AM »

Every model HT is different.  The only way to be sure of the charge time needed is to consult the instruction manuals for the HT or the instructions for the aftermarket battery that you have.  73!

Posts: 1054

« Reply #4 on: July 14, 2012, 09:37:55 AM »

It should take 3hrs 51min to charge a completely discharged battery with your system, but you want to be careful! Go over it by a few minutes and you could overcharge a cell or two and ruin the battery.

The best way to charge a NiCd battery pack is slowly, and at 1.1C over 10 hours. That means a 700mAH battery should be charged at 12V with a current of 77mA for 10 hours, or 70mA for 11 hours. In the olde days, we sometimes hooked up a timer to the charger to make sure we didn't overcharge the battery.  Charging at rates much lower than 70mA meant we could leave the battery connected for longer than the recommended time, but one still didn't want to "overcharge" a battery pack.

Posts: 5030

« Reply #5 on: July 15, 2012, 05:37:09 AM »

If you have a NiCad, use that instead. While NiMH is better if you use the HT every day, it totally sucks if you leave it on the shelf for several days. NiMH loses upwards of 1% of power power day, just by sitting there. If you go 1 month without use, your HT is down to about 70% power.

I go sick of my power tools being dead when I went to use them, and reverted back to NiCad. Now, they seem always charged.

Posts: 6252

« Reply #6 on: July 15, 2012, 05:52:20 AM »

It should take 3hrs 51min to charge a completely discharged battery with your system, but you want to be careful! Go over it by a few minutes and you could overcharge a cell or two and ruin the battery....

That depends on the charging system and how the battery was meant to be charged.  With all the different HTs on the market and the different recommended charging rates for different batteries, you shouldn't make that kind of statement.  What you are describing is an ideal condition for charging--not a specific one for the HT that is being used to do the charging and the specific battery pack being charged--and you should have said so.
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