I've used a 2/12/70 Schmacher with a Deep cycle setting for as long as I can remember. I also had a 2/10/50 but it started charging everything at 15v last year so I pitched it. It too was well over 10 years old.
Either would charge a battery when one of my customers newer "smart" charger with a digital display and lots of buttons wouldn't because the voltage had gotten too low. He wanted to trade and I said thank you but no. I'd be happy to get him a decent charger though if he wanted. He declined.
Return the failed unit for replacement or get something you feel better about. Either way, yours is dead. It happens.