Since I created this post, I have installed the new Lithium batteries into my Hisun Sector E1. It was really not too complex. Here's what I did:
Remove the seat. Remove the panel in front of the batteries (screws on top, and bottom, then loosened the outside panels to make it easier to remove). Then remove the plastic panel over the top of the batteries (you may not have to, but this gave me more room to work). I then removed the battery leads from the 6V batteries. For belt and suspender points, I wrapped the end of the battery leads as not to short anything out as I worked. The battery tie-downs were next and removed easily with a 17mm socket. The J hooks simply fell to the floor as the tie-down was removed (they are easy to put back in place). Finally, remove the batteries; it is easiest to remove the inboard batteries first, straight to the driver/passenger floorboard. The rearmost outboard battery was next, and it has to make a 90 degree turn to come out through the space vacated by the inboard batteries. Then the forward most outboard battery can come out easily. Remember, these batteries are heavy, so watch where your fingers, hands and feet are, as there may be sharp edges inside the battery compartment. Since the pack I got comes with a charger, I removed the onboard charger. Three bolts to remove from the charger from the frame, then pull the charge indicator light from the dashboard well. under the UTV, remove the plastic guard under the floorboard (4 screws), and the wires from the charger go through to the motor controller/battery harness.
Once the battery compartment was cleaned, it is time to install the new batteries. I wished I could have mounted them in the inboard battery tray, but the leads I had were not long enough to place the busbar where I wanted. I mounted the 4 batteries outboard, and made sure the connectors faced inward, with the battery indicator cable on the forward passenger side tray. Since the EAGL batteries are shorter than the Discover batteries, I used a piece of 1/2 inch PVC pipe and a fender washer to take up some room from the battery tie-down to the J-hook. I then ran the battery indicator wire to the dash, using the tunnel under the floorboard. Ziptie or otherwise secure the cable, as the driveshaft is in the tunnel, too, and you wouldn't want the cable to rub on the spinning shaft. With a rotary cutting tool (Dremel), I made a hole for the battery indicator on the dash and connected the wire. Then, to connect the battery to the busbar, I made all the positive and negative connections for the 4 battery leads, the motor controller lead, and the charge lead (all positives together, and all negatives together). I secured all the leads with zipties, and finally make the battery connections. The EAGL batteries have disconnect switches that need to be turned on. They also have blue LED voltage indicators, which, unfortunately, I cannot read since they are too close to the edge. I checked that each pack was on, then finally, started to reassemble the seat/battery compartment.
Turned on the "ignition", put it in gear, and it worked! The gauge in the dash showing amp draw works, but the battery voltage indicator is probably not calibrated for LiFe batteries. With the big battery dot com kit, the lighted battery indicator should show the pack status.
I am still testing the battery packs, but I am happy so far. They allow me to keep speed up the hills (20MPH vs 10 or 12MPH). I haven't done a range test yet, but since the whole cart is nearly 350 pounds lighter, Im guessing that range will be improved over the old batteries. If I do need more range, I can install up to 3 more EAGL batteries before I have to relocate the busbar to add the 4th.
The stock DeltaQ IC1200 charger on the Hisun is really good; waterproof and high-wattage capable, and I wish I could have reused it. There is a way to update the charger to change the charge profile from Lead-acid to Lithium batteries, but there is not (yet) a profile for the EAGL LiFe battery, so I am using the charger purchased from big battery dot com. Perhaps DeltaQ will make a profile in the future...
Remember to wear safety equipment, (gloves, goggles, etc) as you are dealing with batteries. While the Discover batteries are sealed, they are also vented, and precautions should be made in case some acid may have made its way out. Watch for sharp edges in the compartments. Make sure you don't cause any electrical shorts by bridging any positive and negatives as you are wrenching and ratcheting. Secure all wires to prevent chafing, rubbing, or other wear against vibration or moving parts.
Have fun, and good luck if you attempt a similar upgrade to Lithium packs on your Hisun EV!