Dan Burkhart 

Basically, the title says it. Looking to upgrade the battery pack from 36v 7ah SLA to something in the 15 to 20 ah Lithium ion pack.
Will my controller from the SLA pack work or do I need to change that as well?
The SLAs have served well, but I think they are getting near the end of their service life. Not holding a charge as long as they used to.
Thanks

2old

Dan,
If you don't receive an answer here, you might try the Endless Sphere site. Dogman Dan, in particular, is very helpful, and will respond to private emails.

bowlofsalad

Using the search function first is the way to go, I promise you this question has been asked many times in -many- different ways. If you fail to find an answer after a few hours to a few days of searching and reading, make a thread. Then turning to personal messages if you think you found someone who knows the answers to your questions and ask them to comment on your thread. The preferred idea is to share the information and not expect people to answer your questions via personal messages. I am sure the admins of Endless Sphere don't appreciate being spammed with newbie questions, I know for certain some of them get frustrated with the lack of searching and reading done. I am not trying to dissuade anyone from asking questions, but I think there are good ways and bad ways to go about doing things.

As to the original question. Generally speaking, depends on the new battery voltage. So long as the new battery voltage range is similar enough to your old battery voltage range (discharge curve from fresh off the charger to low voltage cut off) it shouldn't be any sort of an issue. Some controllers have a programmed low voltage cutoff(LVC), obviously I wouldn't know if yours does or what that it is if the controller does have an LVC, but this could be something that needs adjusting (assuming you can). All controllers have parts inside of them that can tolerate a maximum voltage, going beyond this voltage will result in basically a broken controller.