I'm having issue charging my Varia HL500. It had been working fine, but now seems to be taking 2 days to fully recharge - until a solid green light. Sometimes the light will switch from blinking green to solid red. I can unplug and replug and get it to go back to flashing green/charging. I've tested multiple charges and cords, all of which work fine for my 1030 and Varia RTL 510. Suggestions?