When I only have one running, no issues but when they both are running, the depth finder shuts off.

I've heard running a 10-2 will work but ive also heard that doesn't always fix the issues.

Anyone else had this issue or have a direction to start.

Voltage or over voltage? This hasnt been a problem for the 4 years ive had the depth finder but just became an issue recently.

After adding livescope ( running a lowrance 9 and 12 and a 12 in garmin) I added a dedicated batter for my electronics ,
I was having units shut down when I started the big motor. All is fine since I added 2nd battery,


MO

If you have not made an obvious change that seemed to line up with the appearance of the problem, then:
1) Your battery has degraded such that it's not what it used to be, and/or
2) You have developed a loose connection or a corroded connection.

Regardless of the above, I will say that electronics tapping into the typical boat wiring harness are challenged by the common use of 16 gauge wire in boat wire harnesses. Installing dedicated power using heavier gauge wire is never a bad idea. (10 ga. stranded marine wire is a good choice)

My units are powered off of the cranking battery.
Way back when, after a little time on the water, when I start the engine there is so much draw that it would shut down my units.
I then added another battery hooked up to my cranking battery to increase the reserve (+ to + and - to -).
That fixed the problem for me.

Thinking of your situation, makes me think:
a) Your battery is old and needs to be replaced or you just need a bigger battery in that spot.
b) There is to much draw on the battery once those pumps kick in. Maybe upgrade the pumps to newer pumps that have less draw on start up?

A proper functioning battery & good wiring harness won't crater from two bilge pumps in a fishing boat, even if there are graphs connected. As I stated earlier, you've probably got a dying battery.

Keep in mind that putting another (new) battery in parallel (+ to + and - to -) allows the weak/failing battery to immediately begin to damage the newer battery. This is NOT a sensible solution. While some do it and find it makes their problem go away, they never realize it's why that other battery just doesn't seem to last very long.

You never said what battery you have - or what outboard you are cranking. That's about like me saying "my truck is making a strange noise; can you tell me what's wrong with it?"