As you say Garry, their models all looked superficially the same and all had the rear carrier battery nmounting. It's good yours has the 250 watt rated motor and I understand they were still good performers with high current controllers. If you have or fit a bike speedo you'll be able to check the assist speed limit of course.
Since battery cells can measure ok for voltage even when dud, the only practical way to check the battery is by riding the bike to see how far you can ride and also whether it cuts out under load on hill climbs. Obviously in trying this stay close to home at first to avoid a long unpowered ride back when the battery runs out, but you'll soon get to know what you can expect.
E-bike range varies greatly, partly depending on the rider's fitness and how much effort they input, partly on the battery size, partly on the controller current and partly on the terrain, so you can see there are many variables.
Hopefully you'll get 20 miles at least and it could be much more.
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I have been on several of our Thursday morning rides now and I haven't had any problems so far although I only use power on the steep hills of which there are quite a few and all seems ok. I think it's a case of fingers crossed for now and decide which route to take if the battery fails. I presume as long as the voltage and capacity is the same I could fit a bottle type battery as a replacement, as they seem the cheapest option.