I have lithium batteries in a number of my bikes, they are very light and being smaller has it's advantages too for making storage room under the seat.
With my Wee I had a full size replacement SSB lithium battery up in the tail, under the seat ready for the original battery to fail, (that original 09 battery is still working.)
The problem I had was the SSB lithium battery in my MT09 failed just outside the warranty period, it cost about 2x that of a lead acid and only lived about 14 months.
I could even live with that but I could not just jump start the bike and ride it when the battery failed.
Each time I started the bike all was good until I removed the jumper battery, I had to keep the RPM's above 3k to stop the motor stalling and then I could hear relays slamming open and shut.
The risk to my ECU was to high so I trailered the bike home.
Not a great position to be in here down under where I love to get off the well worn routes.
As said if a lithium battery gets low it is best to bring it back to life in a slow and controlled way and that is not under the seat of a bike at 14+ volts.
Some of the 19 rides in my shed
2014 V2, Snoopy
2009 Wee, Pumbaa the pig
WR450F, The Blue Postie Bike
YZ250N smoker with rego, Stinky.
Yamaha MT09 (FZ09), The Scud missile.
Club Lead not Club Med.
He with the most toys wins.
Out of my depth in a puddle.
Live life on the edge you will see more that way.
Ridding a motorcycle keeps things in balance.
At the end of each trail and at the end of each day history is made.