Power Wheels SLA Battery Overcharging (Amazon Chargers)

I have a power wheel here for which I just bought a brand new 12v 9ah battery.

The car did not have a charger so I went to Amazon and bought 2 different chargers.

Both are 12v chargers One is 1500ma The other is 1000ma.

I have left it to charge today and the indicator light never turned green. I could hear some slight bubbling and checked the battery voltage. I have read that bubbling in a SEALED lead acid battery is not acceptable.

During charging - 14.5v When unplugged (still red) - 13.6

I immediately went and plugged it into two separate "smart" chargers and the light showed green right away.

Is it just these cheap Amazon chargers? Is that kind of a known thing with these?

I don't really feel safe leaving them to charge until it decides to turn green.

Thanks for any info.