Cordless mower problem
 

I've had my Black & Decker CMM1000 cordless electric mower for about
three years, have had no problems with it, and really like it. About a
month ago, though, it began stopping after about 15 minutes of mowing
(it used to run for 45 minutes with the battery indicator never
leaving the green). I replaced the batteries ($110) and the
transformer ($40), but it's now running down after only five minutes.
The local authorized service shop said they couldn't find a problem
with the transformer, batteries, or PC board -- it ran for an hour in
their shop. I've tried plugging into a different outlet but there just
doesn't seem like there are that many things left that could be
causing the problem. Appreciate any ideas.

David