How to make a USB trickle Battery charger that won't overcharge?

USB devices operate at 5v and 400mA. Can I charge them at 5v and 100mA ,like a trickle charger, and keep the battery from over-charging? is there some kind of ratio battery size calculation to see how low the amps need to be for it to trickle charge? Is there such a thing as a small,cheap, voltage overcharge protection component?

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Re-design7 years ago
From everything I've seen and read on lipos they should only be charged using a charger built for lipos. See this link -
http://www.rchobbies.org/lithium_battery_breakthrough.htm
Even trying to "trickle" charge them could damage them with serious consequences.

Google "lipo battery" and you will be greeted with more warnings etc.
Most cell phones and mp3 players have built in safeguards for charging. My phone and mp3 player that has a lipo battery both can be left on the usb to charge and will quit charging when the correct charge has been met. So you could probably charge them with the solar charger without worry. They should turn off when full. But trying to charge anything without a protection circuit built in or a bare battery might be asking for trouble.
nepheron (author)  Re-design7 years ago
Thank you so much! You are such a nice person to share your knowledge. It's more valuable to me that gold, and so much more useful! -Nepheron
Re-design7 years ago
What kind of battery is it? Nicad, lipo and nmh all have different standard charge rates so trickle rate for them would be different also.
nepheron (author)  Re-design7 years ago
I'm pretty sure most ipods and USB MP3 player have LiPo batteries. does that sound right? I'm making an MP3 solar battery charger.