Well, I have to post this to keep all of you informed. I posted this same thread on another forum. A member there challenged me that this is not safe. After some positing back and forth he finally stated that if the diode goes bad or is defective the battery could explode.
I replied that I was going to test his theory. So sometime this week I will see if he is correct. I don't want anyone injured if there is a problem. Also, if this is a problem I want to post it here. I have been using this charger quite a bit and have not seen anything dangerous with its use. I am going the test this. I will post my results here.
To answer some of the question, John_Mc, when I first made this I just made the extension cord with diode. I added the outlets in a different fashion. I then saw the adapter at Harbor Freight and thought that would work better. There are few ways you can make this.
dcyrilc, the way I understand it is that the sulfation coats the plates and the battery cannot accept a charge. The typical chargers we use cannot overcome the sulfation. That is why they sell these special chargers to try to restore these batteries. The best way to keep the sulfation down is to keep the battery charged.
Today I tested my welder battery after a few days of none use. The thing started right up. This battery is 7 years old, I ran the electrolyte dry and it only showed a 3 volt load test. Something is working right.
Any way I will see how my theory testing goes.