controller setting

Good afternoon.

It really depends on the type of battery you have. For example, you might not want to float a gel any higher, but some types of flooded or AGMs might be able to accept higher charging voltages without damage.

Generally the battery manufacturer has a published voltage for bulk, absorbtion and float. (or at the very least, float). There is some head room in the specs, but I'd recommend that you follow the battery manufacturer's specs. On a typical 12v flooded, that'd be 13.8. The only reason to go above that voltage is if you have stratification in the electrolye and need to equalize the cells. (NOT for gel or AGM)

At a voltage of 12.8V, you're likely still above 90 % depth of discharge... (as in 90% of the energy remains) so it's not that you're doing terrible damage to it's plates letting it sit there.

:-)

Regards,
Nathan