S10 Mike

I really need help on this one...I took my 2 month battery out of old truck and put in my 1999 S10 and scrapped the Ford the only change I would have to do was change the connectors from side to top post,,simple right ?...not in my world. The next day getting ready to hook the battery up notice the positve cable was to short, tugged on it a little thinking it was stuck somewhere...nobe. Need a longer cable. Went to store and got new cable with top post connector ( Black cable cuz they didnt have red, didnt think it would matter ) 4 gauge and a top post replacement for the ground. took battery tray out - disconnect cable from the Mega Fuse and put new cable on...oh yeah I had to shorten the new cable to about 25in or so it was 36in... old cable was 15in. Ok..hooked everything up and no power what so ever...I checked all my work..cleened up the grounds on the frame and body and the big ground on engine..followed positive cable to starter, looking for a link, no fusible links and checked wire to alternator, which is maybe 2 years, looks good and replaced 175a Mega fuse and cable connector thats on 175a fuse that I geuss goes in front off radiator, long cable to the under hood fuse box, cleaned connection at fuse box...OK...I took battery out at tried to charge or get some indication on it but the tiny charger would say 10.5 a which is green light and then spike to 15.6 which is red light, it would jump back and forth like that continuosly, let go for about 2 hours and then the green light was blank on charger, could not read nothing...WOW.....is my battery fried...or am I not seeing something,,,help me if anyones ever had this problem