Can we equalisation charge to Gel batteries?

I wanna ask u guys that can we charge Gel batteries in equalisation as this is a higher voltage charging.

I wanna know this because I installed narada 155Ah Gel batteries to my solar system in which 1 battery is older than other 3 batteries(not much older but just 3 months old) today whole day I charged them via solar and Grid both options selected in my inveret but now electricity is gone and batteries showing just 65%.

So whats the best method to charge such batteries together.