As yet I havnt done a replacement charger for the Twizy, Its not that simple. There is a lot of integration with the onboard Can systems, and so without taking a working unit apart, following the can commands through the charge cycle, (BMS controller etc) and then trying to replicate them its probably just not financially worth while. A repair of the charger may be an option.
A lot of chargers have issues with dirty mains, so never charge from an almost large enough generator, and if you have to use a generator, only ever charge from a 4kw+ sinewave inverter generator. The problem with cheap generators is the spikiness of the wave form, although the bulk of the sinewave is around 230v it can have a 20v spoke on both positive and negative parts of the cycle, so giving a peak of say 270v. And inverter generator creates any old voltage converts it to DC then with an AC inverter creates a (hopefully) pure sinewave regardless of what the generator is doing and its load.
The same goes for some rural power supplies, we suffer a lot of powercuts in the winter, and the supply can be quite spiky (suffolk not the end of the world) . If in doubt buy a simple spike supressor.
I could be interested in looking at a duff unt to see what the options are.
I would suggest , that if the part has a known issue and there is a known relacement that Renault should be encouraged to resolve the issue. Look at your rental agreement, see what it covers, as the Gov grant stipulated certain warranty periods associated with the battery/high voltage side of the vehicle . Renault may still be liable. It may also be part of the Battery warranty. SInce how could they guarantee the battery system if they have no influence on the way the battery is charged. Grey areas are always worth prodding into.
Also could be interested in the remains as one of my customers uses one as a film camara / tracking vehicle, it now has no roof and a 12mm alloy plate front and back, and looks nothing like a twizy. Its got a lot of mods.