Actually there is a possibly bigger difference.
The Ping Battery, (and actually GM has a similar pack,
here:
http://goldenmotor.com/batterypack.htm )
are LiFePO4, instead of the Lithium cells in the
GM Rack Packs.
There was a discussion of the chemistry of the packaged
lithium ion packs that indicated a different chemistry.
(Sadly I can't cite it for you)
I bought the awesome LiFePO4 Product Model: LFP-3615
Weight: 5.1Kgs Capacity: 36V/15AH
This pack includes the
BMS and is in a Duct Tape
package.
I am very happy with this battery.
I installed it inside this aluminum case:
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=36870The case has foam inside to dampen the shock of riding, and
is mounted to a standard bike rack with aluminum rails I cut and
designed.
I installed a toggle switch for Run/Off/Charge and have both plugs
on the end of the box.