Art -

The "brains" in most of these are really pretty simple, but unfortunately it's often very difficult to find out which kind of brain is in a specific model. Most of them are pretty much a "replace black box as required" for a complete module of some sort.

If the batteries are good, and the charger gets them filled up, the most likely cause of short range has to be that

a. some of the juice is going where it shouldn't be going.
b. the motor/transmission is using more of the juice than it should, for what it's doing.

Most of these scooters use a pretty simple dc motor. Older ones may have a "series wound" motor where the current goes through a field coil, then through brushes and a communtator so that the same current goes through one or more of the several rotor coils. If the commutator/brushes get dirty, some of the current can go to rotor windings other than the one-at-a-time where the current is supposed to go. Since the stuff (graphite) that the brushes are made out of wears off, and can "short circuit" the little gaps between segments on the commutator, eventually the motor loses some - sometimes a lot - of it's original poop. If the motor in your scooter has brushes, cleaning the crud out of the slots between segments of the commutator might get it back to better performance. (You may also want new brushes, if you go to the trouble of overhauling it.?)

Most of the more recent scooters that I've seen are using "DC Permanent Magnet" motors, that don't have brushes/commutators. This makes the "brain" that's needed a little more complex, but there is still the possiblity that the permanent magnets in the motor have lost some of their strength. This will make the motor less efficent, so it simply uses more battery output to do the same tripping about. There are, unfortunately, no good ways to test a PM motor other than by seeing whether it "runs like it's supposed to." Measuring current to the motor when it's running under some fairly accurately known load condition may give an indication, but you may have trouble getting the scooter guys to tell you what's "standard conditions."

PM motors are relatively invulnerable to demagnetizing, but it can happen:

a. if the motor gets seriously overheated. (Major-smoke hot, usually.)
b. if it gets "pushed" a lot in operation. Using the motor as a brake is a bit like forcing it run backward when it's trying to go forward. A good design should stand up to most ordinary use of this kind, but it's possible that accumulated wear and tear has "worn out the maggots."
c. if it gets disassembled.

High-efficiency PM motors have strong enough magnetization in the permanent magnet parts that the magnetic field "has to have someplace to go" at all times. In the assembled motor, the other half (rotor or stator, whichever isn't the permanent magnet) provides a closure for the magnetic loop. If the two are separated, the loop closes back through the permanent magnet and it effectively "demagnetizes" itself. Before the parts of the motor are separated, it's necessary to place "keeper" rings/parts on the magnet to close the loop - before the other half of the motor is removed. If the keepers aren't installed, the magnets usually will loose at least half(?) their strength, and it's very difficult to re-magnetize them. Bottom line: if anybody without proper tools and knowledge has "taken apart" a PM motor, it isn't really much of a motor any more - so it naturally will take a lot more juice to make it do anything. A few motor shops may be able to do something with one, but replacement of the motor is the normal fix. Not a cheap fix, usually.

The above are sort of "exotica for your tech guy" probably. I really suspect that your guess - insanity of the controller brain - is the most likely problem.

There are quite a few gasoline powered small utility vehicles advertised as handicap transporters, but they're generally intended strictly for outdoor use. I doubt that you'll find anything gasoline (or propane) powered that most retail shops can allow inside for shopping. In addition to the smoke and fumes, and noise, something on the order of 18 or 20 inches wide is about all most small retail shop layouts can squeeze through the aisles. Shopping carts in large groceries may go up to about 26"(?) but not much wider.

If something that's "outdoor only" would suffice, used golf carts may be fairly easy to come across. A full replacement of the 6 (or rarely 8) 6V batteries commonly used will likely cost nearly as much as you'd expect to pay for a working used cart, and about 2 - 3 year battery life between replacements is common, according to the pros at the golf course. (In my area, used ones usually hit the open market just about 30 minutes before they need a full set of new batteries.)

John