Not according to Energenx manual:
Continued charging, however, with the RenaissanceTM Charger is not recommended for these batteries because of the offgassing that occurs as a side effect of this process. charger is not designed for use with sealed (non refillable) or maintenance free lead-acid batteries. Although it maybe advantageous to use this charger at times on heavily sulfated batteries of this type, consistent charging with this charger may cause excessive venting (offgassing), shortening the life of these batteries.
But since I add water, it should be fine. I am not too worried about the substance in the water since the battery already dead.
If I charge it with radiant 24 hours, I think it can be full in three days. After 4 hours charging today with DC, the standing voltage is 9.98V and 5.51V with light bulb as load which lit rather bright. Good enough for dead battery. The battery feel warm with just this 4 hours....
BTW, this is what I use: