I'm not sure 100% what SLA (lead acid?) is but I wouldent use some that is not recomened for you battery type, as lithium battery are incredibly sensitive.

If it is lead acid then no way do you want be charging it with a charging protocol for the other Chemisty battery and vice versa, lion is way more powerful than lead acid do I'd ditch the lead acid if that's what your using.

The advantages of lion / lipo are more runtime, less weight, , no battery fade, the list goes on.

But to answer your question I don't know if you can buy mulitpal tech bike chargers but in RC you can buy a charger that will charge Lead acid, both main types of lithium polymer, nicd and NiMH.

Also just keeping the wattage the same won't do it, you need to be charging at the right amps, to few and the charge is slow to any and you shorten battery life or risk damage to the battery.

And if I were you I'd get a smoke sector and put it next to your charging station / genraly keep and eye on it. As if its melted together that's a serious and catastrophic failure, and the fact that you slept through that is IMO scary, imagine if it had started a fire. You sound lucky that it dident start a fire.

Tbh you might want to do some research into battery as it sounds like your not to awe are of what your doing no offense.

And lack of knoladge can be a bad thing were high power high campitcy battery's are concerned and even more so with li tech battery's, I mean its not like our charging AAs here.