Today, I passed by a car battery shop and inquired about the latest battery prices. I found out the cheapest battery brand there was Voltec, Century and the most expensive being Amaron (RM400+). The trade in price for the existing old battery is RM25 per piece.
The storekeeper offered to test my car's battery strength to check for wear and tear. He hooked up a device to both terminals of my battery, and the reading came back as 80%, indicating that the battery was still in very good condition. I'm currently using a Century Excel 80D23L, which is around 2 years old.
The battery tester tool used by the storekeeper was from Konnwei KW208 which retails around RM84 at Shopee.
I've seen people use normal multimeter to test battery also so I suppose a multimeter is an alternative tool to test battery strength.