I have a 150 mercury on a legend 186. I'm about to put a livescope on the front. Would an Optima 34 dual purpose be enough for a starting battery and run the livescope/graph ok? Space is limited in a smaller boat trying to avoid adding another battery if at all possible.

No. I tried an Optima 34 for cranking and graphs…it wouldn’t last but a few hours before it showed severe weakening. I’ve since kept the 34 to only crank the motor. Then I added a blue 27 for the electronics only. Then two 31’s for the trolling motor. This is in a similarly powered boat with similar length and weight.

A group 34 is smaller than a 24. The number is misleading on that model. At a minimum I’d go with a 27 but would recommend a 31.

Are the Optima worth the money? I've always ran Walmart batteries an replace them ever couple years. Looking at the Optima now because of ABA discount.

If you will give me the exact model of head unit you are thinking about, i can give you an estimated amp hour usage. Include model, and if you have another depth finder add that model. If you are going to be running on your starting battery you need to think about other current draw elements (livewell recirc, nav lights, bilge pump, accessory items).

But to really do it right you need to do a amp hour calculation on your boat. Here are some ballpark figures. Basically it is (battery size in AH(amp hour) divided by (current draw of your electronics combined).

93SV and Livescope - 19AH for 12+ hours of operation. 30Ah for 18+ hours. 32Ah for 20+ hours.

10" Screen and Livescope - 30Ah for 10 hours. 32Ah for 13+ hours. 48AH for 19+ hours. 

12" Screen and Livescope - 30Ah for 8+ hours. 32Ah for 10+ hours. 48Ah for 15+ hours.


Search online for a battery run time calculator. Note: I added a 55ah duracel agm (sealed) battery in my boat to run electronics. Two things, I wanted a noise free dc voltage to my electronics and I didn't want to deplete my starting battery. My boat setup would have depleted the starting battery enough that it would prob not start the motor after 12 hours (from depth finder and the mega 360 alone). I run power pole connectors on all 4 of my batteries, so I can move electronics to another battery if needed. The charging system on some motors have tons of (RFI: radio frequency interference). Basically a sinewave signal on a dc voltage power circuit. I am a ham operator and RFI is the Achilles Heal to all radio systems . Many people are using the lithium batteries for tools to power their units, which are quick to swap. Might look into this.

Here is a web link that has some specs on amp draw per unit.
Linky

Josh sorry not much help on the battery but interested in hearing about your boat I had a 186 with the merc. Just wondering what year yours is? Not many around I loved mine. I still have a 191 Legend.

In general, Optimas don't have the reserve capacity (RC) to offer the ideal solution for continuous draw applications. There are much better options. If you don't want to upgrade your cranking/electronics battery to one of the big AGM models, I would consider going with a dedicated small lithium battery just to run electronics.

Just installed an Amped outdoors lithium battery for livescope only. Fits in ammo can inside right side rod locker really lite. Take out charge put back in. Works great. Livescope will drain any starting battery.

What size?

I use a 30 amp which is more than adequate, I use a quick disconnect battery connector to take it out between trips for charging. I secure in the rod box with wide velcro (use the brand name) strips.

It’s the 32hr size, might be over kill but didn’t want to take any chances plus comes with charger. Like TR176 said 30 would be more than enough. Same set up used trolling motor plug disconnect bought at academy female end in ammo box lid and male plug wired to 10gauge wire for run. You tube has a bunch of videos on different combinations of installs.

It

It's a 2006. I've had it about 2 years now. What kinda speed did you see on yours?

Awesome! Thank you!

have you seen Impulse Lithiums 16v Electronics battery. I hear imaging is cleared up with the 16v power

https://www.impulselithium.com/product/16v-60ah-platinum-series-marine-electronics-battery/