Like others here, I've had the same experience with a Shorai (and like Mike-TT, did the mosfet upgrade a few years ago).
Originally bought the Shorai in March 2016. One winter, it went totally dead, dead. I used a solar trickle in the garage, but some dips**t kid I let work the two acres here while I was overseas covered the only window with a solar panel in it with a few sheets of plywood (stacked up outside said window). Came back to ALL batts completely dead. Since then I now do 110v trickle along with the solar panel.
Anyway, brought the Shorai back from absolute zero with a "dumb" charger (an old craftsman that doesn't care about s**t, if you ask it to charge a wooden fence post, it says, "Sir, yes SIR!")
I do keep the Triumph on the trickle when it's in the garage, but so far, no issues with starting at all, 7-years on (8 in March 2024). So for the price, it was cheaper than the classic 3-years for lead-acid, outlasted 2-1/2 of those so far. If you're gonna keep your bike forever, then def do the Shorai. When I buy/trade for anything, I plan to maintain it and keep it for life, not toss and burn every few years. Well..., except for relationships with women. Not great at maintaining or keeping those. At all.
PS. For me the seller was the weight. It took about 7-lbs off the bike. Cheapest weight loss of all. Oh, and no acid leaking all over the frame, etc.