Hi, I'm Eduardo from México, my english is not so good, my apologized for that, I'll do my best.

Here's the thing, I ran out of battery yesterday, so I hadn't any other battery to start my savage, so there was this power supply  wich gives 20 A and 13.8 V, I decide to connect to the battery and after a few min. of charging, push the start button. My starter relay suddenly, after some tries of start, died. I alredy replace it and rewire the savage with a diagram founded here but, my battery doesn't keeps the charge. I started and go out for a ride, after 10-15 min. working, the motor just stoped then I tried to start it again and just haven't enough energy, the starter engine didn't make it. I want to check the rectifier, the magneto and the battery.

The battery is new I was told and the sparkplug just changed few days ago, any ideas partners?

thanks for your help!

A 20 amp charger is like 10 times more than the recommended fast charge amperage for our little battery.   Likely your "new" battery is toast by now, do have it load tested before trying to use it for any other troubleshooting work on your bike.  

You can't trouble shoot without a known good fully charged battery to base the tests off of.

Test for the regulator/rectifier and the stator (generator coil) is to read the steady state voltage of the installed battery at rest after you have started and run the bike for a bit.   It should be between 12.6 and 13.4 volts at rest, engine off, generally speaking.

Then you start the engine and with the engine turning over it should rise up be 14.0 to 16.0 volts and that number should rise up towards 16.0  as you rev the engine up in neutral.   Anything over 16 is too much, as then the reg/rect is overcharging the system and needs to be replaced (it will boil out all your water in a short time).

My guess is you fried your regulator / rectifier when you toasted your battery with that killer car super charger.

You need to buy a motorcycle sized charger, no more than 2 amps output.

On my 87 I bought 2 years ago, there were now charging.

1. First check battery... If ok ->
2. Engine running, check what comes out of rectifier with voltage meter... IF OK ->
3. Check what goes into rectifier when running... 3wires... measure each pair (1-2, 1-3, 2-3) thay each should give you the same amount about 100V... IF NOT -> Stator is broken..

I had to change it.

BTW if you indicate the problem to stator, check your wire. They come out under left down cover and go very close by you belt. Due your bike is age of mine, it has already some maintenance history, if wire is not secured the belt contact will cut it. minimum takes a 1 cent piece of electric tape anf you might be there....