This topic is for a EXV4 model built in 2011.

Recently purchased a 2011 EXV4 from auction. It has no batteries, before I purchase a bunch of 8v batteries is there a better option? Prepared to spend more if it results in faster/longer running vehicle.

I am sorry but the only battery type we do recommend would be the type the vehicle was built with. in your case would be the flooded lead acid battery (FLA). 

The two battery types that are considered drop-in replacements to the flooded lead acid are AGM or GEL. The battery charger in this vehicle does have a selector switch for these two battery types as shown here. We do not recommend either battery type. 

AGM, we have used in the past but seen some issues with them and stop using the. The battery charger is only sensing the overall pack voltage. So, when any of the 36 cells within the AGM batteries get out of balance that cell or others will become overcharged. AGM batteries have no way of getting ride if this excess energy so the plates inside will basically burn up and go bad. This will result in a catastrophic failure of the entire pack. FLA can boil the energy off, so they do not have this issue. AGM is typically twice the price of FLA and they are not rated with anymore cycles. 

GEL, we have done testing with but never used in new vehicles. Same size battery has only 80% of the capacity of the FLA or AGM. Cutting overall range. These can have longer life but comes at a cost.

Lithium is our #1 seller now. We never offered lithium in this model year. We do not offer a drop-in replacement for any vehicles not originally built with lithium. In order for lithium to work correctly in an electric vehicle application it has a battery management system which is integrated into the rest of the vehicle. So, the speed controller requires a different firmware. The battery charger is entirely different. The wiring harness is entirely different. Mounting of battery pack is not the same. Dash display needs to be changed. There is a warming system that maintains the battery temp at 50 degrees F. The reduction in battery weight vehicle should be realigned. And with all this as after the fact option can get upwards of $10K.

There may be options available for lithium drop-in replacements for a 72-volt system out there but from our testing these will not work for everyone's application. They can have degraded life when used in an electric vehicle application. Examples of this would be that lithium has higher resistance in colder temps just like any other battery. But lithium cells are sensitive to low voltages so the internal BMS unit will shut the battery off to protect the cell resulting in the vehicle just shutting down. Lithium batteries may say they work in cold temps, but you need to ask at what amperage. Trying to pull 400-500 amps at 20 deg. F more than likely will not work. Also, as the lithium cells age the resistance increases lowing the max amperage the cells can handle. So, they may handle it when new but what about in 1-2 years.

This is where the integrated system comes in. Example the warming system is keeping the lithium cells warm. The integrated BMS is constantly calculating and sending results to the speed controller telling it to only draw so much amperage, so it does not exceed the low voltage limit of the lithium cell. Also, BMS is communicating with the battery charger so it only charges at a certain rate and that it never overcharges. BMS is also making sure all the cells in the entire battery pack are balanced with each other. Among many other things. So, this integrated system is essential for the lithium battery system to operate correctly and maintain long battery life.         

Peak amp draw of the AC drive speed controller is 550 amps. Continues draw cruising at 25 MPH on flat terrain is about 80 amps. AC drive motor is 26KW.

As far as installing a lithium option yourself we would not be able to provide any support on. It would be something you would have to investigate yourself. 

The flooded lead acid is still a battery type we currently build with. As far as batteries go, they still are the best low-cost option for our electric vehicle. We just do recommend going with a high-end brand. There are a lot of so called off-brand ones out there. We have always used US battery part# US8VGC. Another very common one is trojan. For some notes regarding flooded lead acid Click here Flooded lead acid batteries when maintained correctly and especially when you're in a climate such as Hawaii will perform very well. 

But yes, I would recommend in your case to stick with the flooded lead acid batteries.