you folks are making a mountain out of a molehill
if you want to find out if your Shoria is waterproof .. simply dunk battery in a tub of water and watch for bubbles. Just dunked a Shorai LFX 21 for about a minute with balance port cap on. no bubbles came out. that doesn't mean Shorai is completely waterproof, but pretty darn close. note I have not dunked Shorai with balance port open.. that might let in water. but who cares, close your charge port before installing.
if you are really worried about it, simply smear a bit of silicon on all seams. a non-existent problem solved
Earth-X also survives the dunk test with no bubbles. have I dunked both batteries for say 20 minutes ... nope.. then I don't plan on leaving my bike under water for 20 minutes. should I drop it during a deep water crossing.
let's address the real problem that I've seen in this thread ... which is too small LiFePO4 battery used for 990. LFX 18 is just to small for a 990. LFX18 might do the job when weather is warm and your bike is starting with a 1-2 second crank.
LiFePO4 batteries amps delivered drops dramatically under large loads and when temps drop. LFX18 actual amp hour is about 4.6AH. not 18 amp hours as label indicates. almost all LiFePO4 mfg use a PB/EQ rating which doesn't tell what actual amp hour are ... LFX18 fails almost immediately under 200 amp load tests. (details in LiFePO4 testing thread)
IMHO a major cause for LiFePO4 battery failures can be traced back to installing a battery too small. my recommendation for 990 is go with Shorai LFX24 for Starbuck duties. LFX36 for adventure duties to parts unknown. (edit: LFX36 is correct size for 990 but case size is too big to fit tiny battery tray)
or Earth-X ETX24 for Starbuck duties, ETX36 for adventure duties to parts unknown.
for LOTS more detailed technical info.. visit my LiFePO4 testing thread .. link in sig