12VDC light s get dim than brighten ???

Converters will go into storage/float mode after your batteries charge to a certain level, then the 14 charging volts drops back to float mode with effective 13.2v. Depending on how many lights and other things you have on, the battery power can drop back to 13 or less and then your lights may dim. Now it gets a bit weird, you can turn one light off and the power stabilizes or something turns on like a furnace or ac and the converter comes out of storage mode and back into charge again at 14.4 volts. Once it reaches a certain charge it goes into normal/absorption mode at 13.6 out and if there is not a lot of draw or a certain amount of time passes, it goes back to float and then the cycle starts again. I have a fob on my converter that lets me override any of the above modes if necessary.