Solar Panel and Wired Charging Cable Connected Together?

[Kwilk6]

Anyone experimented with connecting both a solar panel and a USB charging cable to a Arlo Ultra 2 together?  This would require some splicing, soldering and sealing the splice against water intrusion.  The solar panels just aren't keeping the batteries charged on four cameras that are not easy to access and I have contemplated running outlets to the locations to correct the issue.  On the downside, if AC power goes down for an extended period there is no way to keep the batteries charged since these are in high activity areas with lots of detection activity.  I am considering splicing the power lead from a solar panel into the USB charging cable from a charging block so that both are able to provide power to the camera whether AC power is available or not.  It doesn't improve the performance of the solar panels, but at least it would provide more reliable service when the AC power is on and keep the camera going a little longer than normal when grid power is down.