Well...
normally you can't swap out that battery but if you're willing to void your warranty, it's totally doable. And as long as we're in the electronics DIY section...
You just need...
-small 2wire connectors
-extra batteries
-an extra 2.1mm recharge port
-
Be willing to void your SF warranty
You would first need to dislodge your internals. They are held very firmly in place. Pull your speaker out of the pommel and pull the battery out. (hopefully your battery wires are long enough for you to access it completely. If not, you're going to have to take pretty much everything out to extend your battery leads.
Anyways, once you are able to pull the battery out, cut the wires to your battery and install your 2-wire connectors to both sides of the battery leads so that you can plug in/out your battery.
***SAFETY NOTE*** when you are cutting the wires to your battery, DO NOT cut through the negative and positive wires at the same time! There is no need to short circuit anything here. The batteries are protected but you don't need to tempt fate and break stuff
Install the same connectors on your extra batteries. Obviously, make sure that if you installed a female connector on the first battery, install female connectors on the spares.
Lastly, take your spare recharge port and install the opposite connector on it. I'm just gonna call that a jumper. I leave mine with my charger all the time. All you have to do is connect the jumper to your smart charger and connect your spare battery to your jumper.
Now you have spare batteries for your hilt with a recharge port.
I prefer to install recharge ports on all my hilts because for normal use, it's way less clumsy and cumbersome than opening the hilt to remove the battery for charging. But if you're at an event/convention/whatever and you're not going to be able to plug into a charger, now you have a solution.
Hope that helps.