Most manufacturers who use batteries don't care if they don't charge them correctly. They consider it a consumable and will likely exclude it from their standard warranty. Battery manufacturers only care if you're trying to make a claim on their warranty. If you haven't charged the batteries properly, they have a way to weasel out of their warranty.

Batteries are a consumable. They have a well known and understood and very finite service life no matter how well they are taken care of.

 

The original battery of the ebike is one 24v batt and it was confiscated in my check in baggage in the airport. Due to less availability of 24v battery here in the Philippines I changed it to 2 similar 12v battery.

My charger looks like yours, but 100-240v ~ DC 24v 1.8A used for 12Ah battery. I've measured more than 24 volt when charging, = for 24 volts & not that it = 24v. Guessing ¾ of 1.8 would = OK for your 9Ah. If I'm right 5 hours OK so my 1.8 A could charge it fine.