I have an IP22 3 Output 15 amp charger fitted to my cargo trailer. The trailer is fitted with three 70ah deep cycle batteries connected in parallel. After using the batteries the charger starts to charge at 15 amps during the bulk charge phase. During this stage the batteries start to boil, the batteries does not heat up but I can hear the bubbling when I put my ear close to the batteries. It sounds exactly like when you put you ear to a can of soda after opening it.
From what I have managed to research about lead acid batteries they should be able to charge at 0.3C, seeing that the batteries are 70ah they should be able to safely charge at a current of up to 21 amps. From what I understand the charger also outputs 15 amp which is then equally split between the three outputs, so that means that the batteries should not be able to be charged at more than 5 amps. I have never had this with my Ctek charger which also charged at 5 amps.
Is this normal or should the batteries not be doing this at all? I know the flooded batteries tend to form small bubbles during charing, but this sounds a bit extreme to be just normal gassing.
Below is a diagram of how my system is wired.
I have also attached a screenshot of the settings I currently use to prevent the boiling of the batteries.
Any help or feedback would be appreciated.