What voltage to worry about the big motor not cranking?

Just looking for info to keep in the back of my mind. NOT looking to throw money at a problem I probably don't have. I'll cross that bridge if I ever reach it.

I have 10g going to the front with a Garmin 12, 10, and LVS34. Just have a Garmin 7 and Helix 5 at the console for now. Livewell doesn't get used and rarely night fish. Battery is a group 31 O'Reilly agm that's pretty new. At what voltage do I need to worry about my big motor (115 SHO) not cranking? I need to meter the battery to see how much voltage drop I have in the wire up front with everything on. This way I'll know what the voltage is at the source by looking at voltage on the front graphs. Also need to remember to throw the jump pack in the boat when I know I'll be out there longer. After 8-9 hours and maybe 30-45 mins total runtime on the big motor my two front graphs were reading 12.1v. I normally start at 12.4-12.5v on the front graphs after the big motor has been shut off around half an hour so I'd assume the battery is close to 13v fully charged. Pulled the front graphs before making a less than 10 minute run back to the ramp so didn't have them in the mounts to compare a couple hours later when I metered the battery directly at the terminals at 12.5v. Maybe that little bit of heat the motor put on the battery that last run brought it up a couple 10ths at resting, maybe not? Obviously the only voltage that matters is directly at the battery when it comes to cranking the big motor.

I suspect there's not going to be a definitive answer to your question. Temperature, and other factors are going to influence how the motor starts.

I understand wanting an answer instead of throwing money at a non existent problem. But....I've keep a Noco GB40 in my boat. (~$100). I've jumped off a few boats on the lake, as well as a few tow vehicles at the landing. For me it's worth the C note so I don't have to worry about voltage. I enjoy being a good samaritan too. Hopefully if I need some kind of help they're be someone there to help me.

Not scientific by any means, but charge up your starting battery fully. Let it rest a few hours. Use a volt meter on the battery. Should be 12.7-12.8. Turn on a console graph and see what it says for voltage. Probably .1-3 lower. Subtract that from what the battery read, then subtract .8 off of that.

So if you have 12.8 at the battery, 12.6 on the graph, at 11.8 you are around 12.0 on the battery, which is about 50% charged. That would be. good time to start it, although you can run an AGM down below 50% as long as you charge it immediately after use without any real degradation in the battery.

Again, not in any way scientific. Just a quick easy way to go about it.

Woody b has your answer. Why worry about it. Use it in the car during the offseason. JMO Bob

I keep my GB40 in the truck. I'll just have to remember to make it part of my pre/post-launch prep. I have 100% faith my 60ah lithiums on my Ultrex will get me through anything I'd be doing. I also plug the charger in as soon as the boat gets backed into the boat shed.

I bought a Duracell Group 31 AGM Deep Cycle from Sam's last year and ran 2 HB 898, 360, 998, Ethernet switch, and Livewell, and after fishing several hours I still crank my '85 2-stroke Evinrude XP fine. I don't think that my front voltage drops below 12.0V (10ga wire on 2 branches from battery to each group of sonars and accessories). Just recently I swapped out the two 898s for an 1199 and Garmin Echomap UHD 93sv on the bow and the console 998 for an 1199 plus added the Livescope GLS10 box to the console branch (360 still on bow branch and ethernet on console branch), and I've not had a chance to run it all together to know what my runtime looks like. While it is interesting that the GLS10 requires a 7.5A fuse, my bench DC power supply shows that it needs much less than that constantly, although it may still be more than each fishfinder alone normally.

Minimum of 10 volts at battery the PowerPoint connection on the motor, cranking the gas motor at all times. As mentioned, there are a lot of variables that affect this.

Another vote here for a NOCO jumper. The GB70 can be used also as a power source when ice fishing for flasher etc. good luck.

From past experience back in my early days of owning a bass boat with a lot of electronics is when you drop below 11.0 v you better be worried about starting your motor.

once again I always had a gb40 or gb70 with me to crank it. I haven’t had to use one since 2019 tho when I went to 2 cranking batteries in parallel.