i just purchased a 2008 Xpress with 90 yamaha. The set up came with an Stayncharge connected to the cranking battery and 2 trolling batteries. i don't get to run the motor too much since I fish local small lakes. When i put an external charger on the cranking battery the first few times it seemed to work great, however, the last time i went to charge the lights blinked for 10 secs, went to battery 2 for 10 secs, third battery, then shut off. When i run the motor to charge all the lights and the charging seems to run fine. Has anybody had this problem before and how can I fix it? Also, what is the best external battery charger to use with this set up?