# Lithium Ion Batter Replacement

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##### New Member
I have a battery-powered unit that needs a new rechargeable, li-ion battery. The old battery had a charging controller spot welded to the nodes and then had shrink wrapping as the outer layer; neither of which I have.
I have purchased a new, exact replacement battery and want to swap the controller. Any ideas on making a good connection on the new battery?
Also, I would like to investigate how to run the unit without the battery at all. Does anyone have a circuit for dropping 12 vDC to 3.7 so that I could run the unit on the power puck? Is this as simple as a bunch of 1 Ohm resisters

#### dknguyen

##### Well-Known Member
Why use 12V if you need to drop it to 3.7V anyways? Use 5V or 6V instead. Or even a 1-cell Lithium Battery which falls around 3.7V anyways.
Wait, what's a power puck? Depending on the current required a linear regulator may suffice. But higher current levels need a switching buck converter since linear regulars waste energy and produce heat dropping 12V down to 3.7V

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##### New Member
A power puck is the 120 vAC adapter that outputs 12 vDC. This came with the unit and requires not additional purchases. I can live with the heat but I do not have the diagram for a buck converter. Thanks for the response.

#### RODALCO

##### Well-Known Member
We have these 3.6 Volts Li Ion batteries in data loggers we use as back up for the memory settings. (they supposed last between 5 and 10 years)

If they get replaced and don't have the flying leads, carefully scrape/file the ends of the battery to make the solder grip easier.
Quickly solder your jumper leads on with a hot iron. wear safety goggles just in case.

##### New Member
Thanks for the tips!

#### RCinFLA

##### Well-Known Member
Cut the spot welds and solder onto new battery. LiIon requires a complex charger that is constant current, tops at 4.2vdc, then terminates charger when current drops to low value.

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