Unpredictable power loss on a Viking E-GO

[lemelman]

I've just joined the forum in the hope that someone can solve a problem I'm experiencing with my Viking E_GO folding electric bike. which I've had for about 5 or 6 years. I'm in my 80's and haven't really done more than about 500 miles or so. A couple of months ago it suddenly lost power whilst I was riding home and the lights on the handlebar controller went out. I pressed the power button on the handlebar controller, power was restored and I continued to home with no further problems. There were no problems on the next few trips, but then it happened again, and again pressing the handlebar power button fixed it. A week or so ago it happened just about as soon as I started from home, but this time pressing the power button had no effect. I switched the 'ignition' key off and on a couple of times and the handlebar power button eventually became active and I continued with my short journey. There were no further problems with that short journey of about 2 miles.
There's clearly something wrong, so what should I look for?
I have an extensive workshop and know how to use tools and machinery.
The bike is the one with the controller underneath the sliding removable battery.

 

[Nealh]

Either the battery age at 5 /6 years old or the ignition switch may be faulty.
I would normally say the battery but first would resolder the igniton wires in case of a faulty dry solder joint or simply fit a new ignition sw, sw contacts have been known to cause issues.

 

[lemelman]

I've actually got two batteries, one only 2 years old, and the problem is apparent with either. If it's a faulty switch, how could pressing the power button on and off have any effect?