Charging 2*SLA battery from Solar

I have an application that requires 2 12V 7.5 AHr lead acid batteries to be charged from 2 nominally 12V but actually nearer 18V with no load 1.5A solar panels, in the end i hope to get away with 1A solar panels but first I need to accomodate 1.5A panels.
I don't just want to put a diode in series for risk of overcharging the batteries.

If I could find a suitable charge controller at a reasonable price I could buy them in, but I cannot find one.

so looking at building something, I have PIC in circuit anyway for other reasons, I am considering PWM'ing the solar output to keep it at 27.6V but this area is new to me, indeed I am not sure this is the best approach, any ideas on whether this is a suitable approach or if not what is?

Pete D
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