You go to your powerchair or scooter and plug in the charger and the error light comes on. Or the charger doesn't start and does nothing.

There can be several reasons for this. I will start with the most common.

a) Your batteries are too flat.

This may be because you didn't use the chair for some time.  And assumed that it would be fine. Its not!  The batteries in your powerchair naturally discharge over time. Some faster than others. 

If you don't use it then charge it at least every 2 weeks overnight without fail. Or battery damage may result.

And even when switched off, your powerchair itself also still takes a small amount of power from the batteries.  Or maybe you left it switched on by mistake for a day or so after you last used it.  Clue? Powerchair may not turn on...

The odd thing is, many powerchair chargers will not charge a very depleted battery. If your battery voltage falls below a pre set limit then the charger just refuses to play the game.

The solution in this is the case is simply to connect your Wheelchairs batteries individually (one at a time!) to your cars battery with jumper cables and start the engine running for around 20 minutes or so. 

Or connect directly to an old style transformer battery charger for the same length of time.