Hi Mick,
I don't see any problem with the battery, please check these "facts" for yourself but I understand the entire car has a 5 year / 100k mile warranty and the battery is warranted for 10 years which is extended to 11 years if you have the "Hybrid Health Check" done as a free part of the Toyota dealer service. The health check can also be done (chargeable?) by a dealer if you have it serviced by an independent garage. Remember it's basically Prius running gear and many of them are on starship milages in the hands of cabbies with very few problems. No turbo, no Dual Mass flywheel, no clutch, no Diesel Particulate filter, no starter motor, no alternator, no drive belts.
What it's like to drive only you and Mrs F can judge. Mrs S would never want anything else except the Yaris or her own full electric car (Peugeot Ion). Do have a good long drive to try it.
Around town it runs mainly on battery but you are not really aware of the engine cutting in and out. There is a dash light that indicates if you are using battery or engine. It is capable of running battery only up to 43mph but uphill or hard acceleration soon fires the engine up.
When I bought mine (new) in April 16 I enquired about a tow bar but there didn't seem to be one for the Hybrid version. I now believe there is one but only for fitting cycle carriers and not actual trailer tugging. But please check the latest facts. My bike fits inside easily with the seat folded, front wheel removed, and my mates bike too, so I haven't bothered any more.
The Toyota owners club (independent not linked to Toyota UK) is pretty good for questions and research. By paying to be a Premium member, about £16 per year, I get a 15% discount card for Halfords which is well worth my while.
Steve