For battery cells checking, a hydrometer is required. You can take the battery to a battery shop (after full charging, ie. charging for a long time after load shedding). An the guys can check the gravity of all 06 cells. They can also put a meter for load test to tell the battery condition.
But only do it if the battery is really reducing water drastically. If you have to top it up every 5-6 months, it's fine.
A faulty battery would reduce water level below minimum within 1-2 weeks. Keep checking the water level every few days. If it doesn't reduce much, nothing to worry.