Lee Iacocca, EVG or EV Global e-bike/ebike --36volt ... new battery time

I bought this for my wife, child and myself about 2-3 years ago. It had a new SLA battery, it worked find.
I added the xtracycle to it--and it really works well for us. It is wonderful. Well, it was.
This last winter killed the SLA battery. Time for a new battery.

I'm also thinking new chemistry as well for the battery.

I've read a number of forum posts here (most dating from 2007-8) that talks about options for
batteries. I'm wondering if any of this has changed. My big questions:

a) If I want to add batteries to my current 'case & charger' that holds the actual battery cluster,
if I get nickel hydride , nickel cad, or lithpo batteries, will that charger still work?

b) I've had a 'trickle' device on my SLA battery to keep sulfate crystal growth down (and I'm sure it
extended the battery substantially). "power pulse battery management system' is the name of the device.
Do I need to disconnect this device once if I go with a different battery chemistry?

c)finally...I read about how the ping lifepo batteries on ebay (atleast on the 2008 forums posts) are the best,
but they don't fit the evg battery case well--or at all?
Has anyone modded their 36v evg bike to allow them into the battery case?

any other opinions? I know some feel--since it's an 'orphan'-- that it is a money pit. I haven't found that
to be the case--I hope to get this battery switch out and really see distance increase, etc. With the xtracycle,
it's amazing. Like an electric van with pedals.

Thanks ahead of time for your replies. :)
-v