Electric problems on my Geo

Hi guys, i need some help here, I have a Geo metro 91 and I had this problem, on Saturday, I was driving back home and suddenly the radio turned off, the lights went down and the battery got discharged, the fule injection stop working and i had to tow the car to my home
I took it to the shop and they checked the alternator, they changed the carbons and they test it and is working ok
they gave me last night the car, so, i was driving and I had the same problem, i called the guy and we put another battery and worked and i turned off the radio, removed the battery and the alternator was working

Here is my concern

I put the radio one week ago, could the radio make a circuit that crash everything

also I checked the battery and the water of the battery is low
if the battery is damaged, could the battery create a circuit and crash everything
any ideas , I will really appreciate them

As long as the radio circuit is fused, if the radio were to short out, the fuse would blow long before you'd see these kinds of problems. Even if the fuse holder was shorted with a penny or something, you'd still smoke the radio long before you'd get charging system problems. The only time i've seen problems like this is when a heavy gauge power wire gets shorted to ground, causing a low voltage condition in the car. However, these conditions are quickly followed by the car being full of smoke and, eventually, flames, if the problem remains uncorrected for a few seconds. It sounds to me like there's maybe a bad ground from the battery to the chasis, or maybe a bad power wire from the battery to the alternator. It never hurts to replace all the chassis ground wires (from battery to chasis, from chasis to block) as well as the power wire from alternator to + battery terminal. Use a good quality wire. I used 4 gauge wire that you can pick up at any car audio shop. This is bigger, more flexible, and will stand up to abuse better than stock in most cases.

Sean, thanks very much for the tip, i got it resolved, the alternator wasn't developing all the charge need it by the car, so, the alternator was repaired and seems to be OK now

thanks again,
By the way, nice picture of your car