Operating fish finder using lithium battery

[wiperhunter2]

Wiper hunter you should charge both batteries to full chg. separately, then wire them together in parallel let them sit at least over night that way to balance them so they are equal. Then hook them up in series, that may help. Supposed to do it first the time and periodically to make sure batteries are equal.
When I was having issues with one battery the factory told me to do that and said it could resolve the problem and will make the batteries work better.
Good luck.

Thanks Mildog, hopefully that will work, it's worth a try and it makes sense. By the way, here is one of the batteries I'm using.