For those of you that have gone the route of Lithium batteries, what battery did you use for your cranking battery. I had ordered a FuelZero 100Ah battery for it and was told by the owner of the company they are really not designed for cranking because they have a max of 130 cranking amps and for only a few seconds. If its longer than a few seconds then the BMS on the battery will disconnect the battery. I did a little research and most places say the 250 ProXs requires at least 130. I am wondering if this is why I've heard stories of cranking batteries being absolutely dead on some boats out of nowhere.

relion hp100 made for starting

ionic 12 Volt 125AH Battery - 12V Lithium Battery
This is the battery i use on my pro xs 250
and three 100ah for trolling.
starts mine ok

I believe the Mercury Pro XS 250 specifies 1000 MCA. Whether you're quoting 130 MCA (rating at 32 F) or CCA (raing at 0 F), you're nowhere near what Mercury calls for. You will trash an expensive Lithium battery in no time trying to make it into a cranking battery. Lithium does lower deep cycle drains much more readily than short-term high amp loads such as the starter for a motor. Some companies offer a "heavier duty" lithium battery as serviceable for starting, but it's a challenge for the technology I won't invest in, and that might be worth noting as I'm an electrical engineer. Quite a few guys "go lith" for the TM, but NOT the starter. I'm one of those.

I run an RB80 Relion and it gets the job done..it’s never had the BMS disconnect and it’s ran 3 12’s pumps, poles, etc..but I can tell I’m tasking the hell out of that battery. It takes 3 times as long to charge as the same trolling batteries. I’d be confident with one of the Relion 100RB HP versions. If I had it to do over again..I’d stay with a Quality AGM for the cranker and lithium for the trollers. If my charger wasn’t completely reprogrammed for lithium...I’d switch now. I’ve been running lithium’s for over two years.

As i stated above, I have used the ionic 12 Volt 125AH Battery For about 8 months now, Made it thru the winter months with only one issue. It didn't like very cold weather, below 40.. It would trip the BMS the first time i tried to start the motor. 30 seconds later it would start. I learned to turn my graphs on before i launched and that would heat the battery and it would start and run all daylong, i actually only charge them every two trips, still use the minn kota 440 charger.
I also run three solix 15 and 12 and 10 units along with a 360 mega.
I also just added a Ionic jump box, that will take care of any low battery warning once detected.
Lots of information over on BBC take a look at the electrical thread and there enough info there to make a good choice for your application.

If your asking about a 250 ProXS 4 stroke I would highly recommend getting a 31 series AGM.
After reading all the stuff from Mercury and reading a ton of information on the internet. I sold my 125 ah lithium and bought a NorthStar 31 AGM.

This is what I use as well and it’s done well for me for nearly a year now.

Dean, I run a big AGM for the main battery as you now would prefer in hindsight. I charge the lithiums from a separate charger, so I pulled the original mega-heavy 4 bank charger from the boat, saving yet another 30 pounds. For the AGM I now use a NOCO Genius 10 charger (a new model with their latest technology). It's not a marine onboard charger, but it does have an IP65 rating (dust tight, water jet protection, just not submersion). That charger costs ~$100 on Amazon, should you ever wish to consider moving back to AGM for the main battery.

Thanks for all the feedback guys. This confirmed a lot for me. It appears several don’t think the current lithium batteries should be cranking batteries including the owner of the company I originally purchased from. Not sure what to do now but I’ll figure it out this week as I need to replace my cranking battery

I have run the the Relion lithiums for about a year and a half with no problems what so ever. The 100 hp for a cranker and the 100's for the trolling motor. The 100 hp puts out 850 cranking amps and the 100's about 200 amps, not enough to crank an outboard. I run one solix, two helix and a panotix all day with no problems. I also happen to sell the Relion brand along with all Continental products, Trojan, Odyessy, Optima, etc. Trojan came out with with a 400 amp cranker called the Trillium. Works ok with a trolling motor but cranking a big outboard is a little shakey.

Odyssey pc2150, x2, or the Northstar for cranking/dual purpose. The Odyssey will pulse 2150 hca and 1150 cca....

There are some companies who offer a beefed up lithium that can be a cranking battery (as I said before). Many lithiums are geared toward off-grid solar energy storage, and this is the leverage point for the lithium batteries suitable for trolling motor use. Some have tackled the challenge of offering a lithium cranking battery and some have just let that application go. I didn't mean for my prior statement to say it won't work, but you have to get the right one for it to work, and there aren't as many of those on the market.

I'm using the Relion HP100 as well and have had no issues. I'm not powering up a big 250hp with 4 graphs, (Rather a SHO175 with console 12" and bow 9") but I have had no issues so far.