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How to convert a battery pack to AC power?

Wife owns a very expensive piece of Japanese cosmetic device that uses a very special Li-ion battery pack but the battery died! No way I can find a replacement for the battery pack and I am wondering how to convert it to an AC power?

I have no experience doing this at all, so if you can provide as many details as possible, that will be great!

The battery pack:
3 wires connected to the connector: red, black and yellow; 7.4V, 750mAh

The AC adapter used for recharging the device:
INPUT: 100VAC 50/60 Hz 8VA
OUTPUT: 9VDC 500mA

Thanks a lot!

Picture of How to convert a battery pack to AC power?
adapter.jpg
frollard4 years ago
is that battery by chance 40 x 69 mm?

Seriously it won't be hard to find a replacement battery...it does not have to be the same mAh, just voltage - As steve says it's likely compatible with many mobile phone batteries.
http://dx.com/s/lithium+7.4 shows a few contenders - just needing the 3 connections (you may have to solder your wire on the 3 terminals carefully.

As for replacing it with an AC adapter, just as before, if you apply 7.4ish volts to the battery terminals inside the device it should power up. Don't apply much more voltage on the battery side because there may be lithium protection circuitry that gets really mad at 8.4 volts. The yellow wire is just temperature sensor - and the device may or may not function with it connected (it may sense a defective battery if the temp sensor isn't there)
samaddon4 years ago
First of all you need to know some thing about electronics.
Now come to the point . Check weather the battery is completely dead or not if you are sure cut the wires of the battery . Consider the red and black wires the red one is the positive and the black one is the negative and the yellow wire is not for consideration. Just connect 5 , 1.5 battery together in series and connect the positive side of the battery to the red wire and the negative side of the battery with the black wire! HOPE IT HELPS
That actually looks like a pretty standard mobile phone style battery to me. I'd take a look at one of the battery replacement websites.