New battery

[b1k3rdude]

Hmmm, have alternators on bikes changed that much?
I'm checking with a mate who has built his own electric bike and will let you know what he thinks.

Your not seeing the larger issue fella, Lithium batteries typically need an intelligent charging system (Charging Algorithm that monitors and analyses), in simple terms - 

1. The charging system will start supplying constant current.
2. then it will then ramp down the current and switch to constant voltage mode.

Now LiPo4 might be different and the following link suggests it should be possible use these as drop in replacements with caveats -

https://earthxbatteries.com/engine-charg...-batteries

Spoke to yamaha Uk and there is one bike on their roster that has a Lithium battery the yz450f, but this also comes with a separate external charger that is required if the battery voltage drop below a certain amount and enters sleep mode. You have to remove the battery, use the aforementioned charger before putting it back on the bike.