21v 1 amp Li charger.


Well-known Member
I bought this charger off Amazon.

Lithium Battery Charger, 21V/1A Adaptative Lithium Battery
Charger,Thick Copper Core Li ion Charger Adapter


I used an adapter and soldered the charger wires to the adapter.

This battery was charged using a Dewalt 20v charger.
Dewalt charger stopped charging at 19.4v.


The new Li charger put 21.4 volts in the batteries before
shutting off.

I'm not worried about fires. The Charger only puts out 1 amp.

This is my second charger 21v charger. I am using the first
charger at my other location.

I think Li batteries will last longer if they are fully charged.

Time will tell if I'm right.
George, it's my understanding that frequently charging Li-Ion batteries to full capacity will reduce their service life. Which might explain why your purported 20 volt charger stops at 19.4 V.
Time will tell if pushing the cells to 4.2v hurts or helps.

I know if a cell drops below 3.6v (18v) the dewalt charger will not work.
I had two batteries I had to take apart and charge each cell to 4.2v,

I'll let everyone know what happens.

I try to stay away from battery talk. Anyhow... Lithium battery will last longer if charged before they go down where they no longer power the tool. The reason is that the longer it takes to charge them, the more heat is generated.

One way this happens is with the inadequate-cheap charger. A proper charger will not overcharge them. There are GOOD chargers that have a temp setting, they will charge until the setting is reached regardless of charge rate or voltage.

A 20 volt pack will charge to 21 volts, 5 cells @4.2 volts. Charging them at full capacity does not hurt them, but charging them to a terminal charged voltage of 2.1 volts will double their life.

Charging them @ 4.0 volts will again do the same thing. I do have a charger that will charge by temperature setting, but never bought the adapter, as I am there during the charging process.

This charger is designed to charge individual cells to 4.2v - 4.21v.

I first charge with a dewalt charger and bring the voltage of a 20v battery up to 19.4 to 20.4v, then slowly top off with the 21v Li charger.

So far so good.

Lithium batteries should not be charged above 105 degrees F., as per OEM recommendation. I prfer to charge 4them ONLY to 105 degrees F. Charging them to 4.1 volts will double their life cycles. Charge them to 4.0 volts and would double the life cycle again.

The chargers that come with the batteries strike a happy medium, between fully charge and heat.
The batteries last long enough pass the warranty date, but, like I said, charging them to a lower end of charge voltage, will greatly extend their life. NOw you know why I get some much life out of my betteries them most.

You will find out, as I have a few years back, That a totally discharged Lithium cell, usually loses capacity. It will never come up to full rated amp hour ratings it had when new.
Charging them as you are doing, As I have been doing for years, certainly makes an otherwise junk pack useful again, BTDT many times.........

I took an 18v dewalt battery apart that was dead for many years and brought half the cells back to life.

They are Li not Ni-Cd. I had to buy a dewalt charger to charge it.

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