I will be going to a higher voltage sometime in 2011. The battery pack is a bit over three years old, and will need to be replaced within the next year as it is showing signs of age.
Apologies in advance for the long post
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The original Citicar setup used eight 6-volt batteries for 48 volts which made the Citicar weigh about 1,300 lbs. I am presently using six 8-volt batteries to save weight as my normal use of the Citicar is well within the range of six batteries (24 miles or so - I usually drive about 10 miles a day). With six batteries, it weighs 1,160 lbs on the local truck scales. A ten battery 6v/60v setup would be difficult to implement due to space constraints, and a five battery 12v/60v setup probably wouldn't have enough range.
Keeping with six batteries, I can go to 72 volts using 12-volt batteries.
↑ Increases speed to at least 45 MPH. Increases acceleration, which increases fun quotient. (Due to differential gearing, the top speed of the Citicar is about 45 MPH / 5,000 RPM, and 72 volts would reliably deliver the max RPM the motor can handle.) (-$200; six batteries instead of eight)
↓ Problem is that it will cut my range down somewhat, perhaps to about 18 miles, less if I routinely drive around at 45 MPH. As the pack ages, the range will decrease, and I may not be able to reliably get to work and back after a year or so. Replace battery charger and defroster fan ($600 - $200 = $400).
Although a nine-battery, 72v setup would increase the range significantly (36 miles) or a 12 battery 6v setup (60 miles) it would be a pain to implement in the Citicar, and would increase the weight a bit too much, making it slow to accelerate even with the higher voltage. Besides, sitting in a Citicar for more than an hour to actually use that amount of range would be a bit masochistic.
If I go back to eight lead-acid batteries, there are four options. (lithium is still too expensive) All involve moving the controller back to the OEM position behind the passenger seat, and increasing the vehicle back to OEM weight -
48 volts (eight 6v batteries) Easiest and cheapest.
↑ Increases range to about 40 miles (6v batteries have more aH capacity).
↓ Slower acceleration and no speed increase.
64 volts (eight 8v batteries)
↑ Increases range to about 32 miles. Increases speed to 41 -43 MPH (guessing 2.5 to 3 MPH gain per 8V battery)
↔ Acceleration about the same - increased weight balances increased power.
↓ Have to replace battery charger and defroster fan (both 48v items) - about $600. All costs are the price beyond the cost of the battery pack.
96 volts (eight 12v batteries) Would need major changes to realize potential.
↑↑ Potential speed increase to about 55 - 65 MPH. Faster acceleration.
↔ Keeps range at about 24 miles (12v batteries have less aH capacity than 8V).
↓↓↓ Have to replace battery charger, controller, defroster, AC/DC converter - about $2,000. Also would have to replace the transaxle/differential and motor to realize potential for a total of $3,000 - $5,000.
192 volts (eight 24v batteries)
↑↑↑↑↑ Potential speed increase to 100 MPH+. (Like anyone would want to go 100 MPH in a Citicar!) Much faster acceleration.
↓↓↓↓ Decreases range to less than 15 miles. (24v batteries don't have much aH capacity) 24v batteries are more expensive, and would have to replace all the parts as with a 96v setup. $4,000 - $6,000.