An alternative would be to buy a higher amp (60 works for me) Progressive Dynamics converter and measure charge voltages interrupted by cold beverages. Any AGM battery will gulp amps for the first part of the charge cycle and then sip up the final charge at it's own pace.
Yes, a fixed output charger would be the best but how many minutes out of a charge cycle are going to be used at the higher output? A method for doing this that may be more efficient, economically, is by using a power supply.
For me, solar does the heavy lifting but I also have a PD converter that is 45 yrs. old and working.