My electric bikes are home made if you like, just normal mountain bikes with add on motors, I have quite a few, my main daily rider has a BMC geared hub motor (rated at 250W) I run it at 10 times that using a modified controller its good for 30mph and will climb any hill, I use model plane Lipo batteries to run it 48V 15Ah in total and charge it from a model charger, don’t monitor any cells just run a battery meter and power watt meter to ensure I don’t over discharge it.
It has been very reliable (they have all been very reliable) you can get some decent off the shelf bikes now, there are a lot on Ebay some good some bad, whilst not strictly legal on the road you can still be sensible, I have never had any problems in over 10 years, I do have a switch that limits the power and of course only use full power off road… ahem.
Ebiking on a modified bike is almost as much fun as a Leaf oh and watt hours per mile, with light peddling I can get 20 watt hours per mile, that’s pretty efficient.