How to attain a topping charge for a lead-acid battery?
Generally speaking, the topping charge is done by keeping the battery voltage at the equalize voltage until the current drops to some fraction of the charge current. 

I've built several simple lesd-acid chargers over the years but mine are two-state chargers - the charger drops out of equalization mode when the charger drops out of constant current mode. 

It would be easy to add a circuit that keeps the charge voltage at the equalize voltage until the current drops to perhaps 10% of the constant current value. You do need that threshold to be higher than any current that your circuit consumes. 

I'll have a look at my most recent charger version and see how easy it is to do