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Poor battery charging rate

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1 Poor battery charging rate on Wed 24 Nov 2010 - 13:27


Maybe its the incorrect charger for the battery, a 8.4v,1800mah li-on, but I've noticed that a full charge isnt really that when you boot up again and look in the power info in control panel.
Mostly I see a figure of 63% full, so when I stuck a meter on to check battery use, I also looked at the charging rate.
My device charges at a low 0.5Amp, which isnt really the problem even though the charger says 1.5A rating.
The problem is that it switches off after 1hr 30min which is definitely not long enough to fully charge the batt, ideally 3hrs plus is what is needed.

Solutions? confused

I pull out the charger and plug it back in again 3x to get bigger capacity.
After the 1st charge from dead flat, which took 1hr 30min, the batt was only reading 8.2V on the meter, the next charge was finished much quicker in about 30min, by then it was time for bed and work in the morning. retests some other time.

Since testing the charging rates,I can no longer recommend the above method of 3x due to the fact that after a week of doing this the battery now reads 8.53V after the 2nd charge is finished.
This practice can only damage the battery or reduce its lifespan in the long term.

The big caution here is that Li-on batteries have very exact charging needs and the battery can be damaged by using the wrong charger/ charge rate.
e.g. I have a charger for a 7.4V 1100mah Li-on and I wouldnt even think of charging a 8.4v batt with it.

In other words dont use a 12V lead acid charger meant for a car battery.

Anyone else with any ideas or observations?

Last edited by blujeenz on Mon 29 Nov 2010 - 11:51; edited 1 time in total (Reason for editing : new tests and new info)

2 Re: Poor battery charging rate on Wed 24 Nov 2010 - 14:40


Hmm, haven't noticed any issues regarding charging, but yes it discharges quick to 80% after disconnecting. I will try to read the voltages when full(mine is marked as 7.4V 1800 mAh).

Full - 8.5V (4.25V on cell)
Discharged - 7.4V (3.7V on cell)

Seems completely normal for Li-ion.

Do you charge it when netbook is off? I have noticed that there seems to be some charging code running when netbook is off, because while charging and shortly pressing power button I am able to stop/start charging(battery LED) without disconnecting charger.

Strange that nominal voltage for your is marked as 8.4V, it means 2 cells in parallel with voltage 4.2V, interesting what chemistry it is as normally it is around 3.7V for Li-ion? Seems overestimated. The charging voltage should be around ~9V.

Last edited by otoluk on Mon 3 Oct 2011 - 23:18; edited 1 time in total

3 Re: Poor battery charging rate on Wed 24 Nov 2010 - 17:36


Mostly I charge with the netbook off, but sometimes I just leave it charging while busy.

You're correct the charger does push out 9v. I seem to remember the RCplane batts were 2s lipo's which could be charged upto a max of 8.4V.

I think these chinese batteries are being rated according to their max ultimate volts which would be 8.4, even though the standard or nominal voltage is 7.2V.

They have a different way of doing things. Smile

4 Re: Poor battery charging rate on Mon 3 Oct 2011 - 23:24


The battery for my netbook has only 2-pins, so it is missing 3rd wire which gives precise measurements. So the netbook can't read the remaining capacity very correctly. Because of this it seeems it is normal that battery charge in percent drops very quickly the first moments after disconnecting charger.

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