HTC EVO 4G Forum

Accessories Universal external battery charger question

I just got my extended battery and external charger from ebay and I'm trying to figure out how long it will take to charge my battery. The charger says output: DC 4.2 ~ 350ma~+/-50ma

I thought that meant it would take 10 hours to charge a 3000mah battery but that can't be right. How long will it take to charge a 1500mah and a 3000mah battery?


#1 novarider, Jul 31, 2010
The charger will not charge your battery to any kind of speed. You are both s
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hort on volts and amps. You need atleast 5volts and 500 mA. The charger can not provide the proper electrical range. I would return the charger and try to find some that match the requirments of you phone. If you use the charger it will either not charge your battery fully or it will cause the battery to malfunction.

As for your question about charging time, you have to understand that a charger inputs 5volts and 500mA-1000mA. The phone converts that to a stored charge of 3.7volts and 1500mA. The time to charge has way to many variables, for example, temperature, change level, and plate charge set. Long answer short, it should take about 4 hours with a noprmal charger.
#2 RiverOfIce, Jul 31, 2010
4.2v at 350ma is about equivalent to 400ma at 3.7v (RMS/nominal voltage of li-ion poly batteries) in total charge movement. Li-ion poly batteries charge at nearly 99% efficiency at 1/10C-1/4C charge rates, which these are charging at.

Therefore, the 1500mAh battery should charge in about 3.75 hours, and the 3000mAh should charge in about 7.5 hours, assuming they are both properly rated for total capacity and charge from the cutoff voltage (empty) to full charge with no trickle-rate top-off, as well as an exact 350mA 4.2V charge rate.
#3 axisofoil, Jul 31, 2010
Its an external battery charger like the kind that seidio sells. This is what I bought 3000mAh battery + dock charger for Sprint HTC Evo 4G - eBay (item 320566610900 end time Aug-01-10 09:44:53 PDT)
#4 novarider, Jul 31, 2010
It WILL charge the battery, but it will take about 7.5 hours to charge it from empty to full.
#5 axisofoil, Jul 31, 2010
It is a dual charger at 5v 800 mA. Which means it could charge the 3000 battery in about 5-6 hours.

axisofoil- I do not know you but you can not just shoot out numbers. A battery should never be drained to empty. The htc evo also requires a minimum of 5 volts. Sorry that is spec. The charger he stated has two charge levels, which will work for his battery.

The 1500 will charge just short of 3 hours, the 3000 will charge just short of 6 hours. Depending on many, many, many conditions.
#6 RiverOfIce, Jul 31, 2010
How many volts should this battery be running at? I have a battery app and it says its at 3.994v is that high enough?
#7 novarider, Jul 31, 2010
I'm not just shooting out numbers. The EVO itself may require 5v. That charger does NOT charge through the phone. It is a standalone charger with a USB output. The spare battery slot and a USB port. The 5v 800mA is the USB port, while the 4.2V 350mA is the battery slot.

The batteries should run between 4-4.2V (Full) to 3V (Empty). Full charge is slightly different voltage depending on the exact chemistry of the pack.
So 3.94 is just peachy.

You would be best off charging the big battery in the phone with the AC adapter that came with the phone and a usb cable (will push 1000mA at 5v). Although technically you could charge it faster using an RC lipo charger... but you probably shouldn't as that can get quite dangerous... fast.
#8 axisofoil, Aug 1, 2010
I have an rc lipo charger since I drive a business rc truck. Only problem is I have no way to hook it up to the charger.
#9 novarider, Aug 1, 2010
Would you use this charger to charge the seidio 3500mah battery?
#10 novarider, Aug 11, 2010
Yes, you are quite right about the full charge taking no less than 7.5 hrs using the numbers provided. I was reading your post, trying to determine if my battery was a dud, when right at 7.5 hrs the indicator light began to glow blue, indicating a full charge. I plan on leaving it on additional time to make sure it's topped off. Thanks for correcting the other gentleman who inaccurately stated it would not charge. :)
#11 Freud54, Mar 20, 2011