JMT battery replacement question

Hi,
I have one of the JMT diesel engines, the Alco PA diesel AA, in Santa Fe colors, with a version of the Proto sound system. The system is capable
of sounding station announcements, horn, etc. Apparently the battery is down and should be replaced, and I understand that a Radio Shack PN 23448 Ni-CAD can be used provided I tape some insulation around the case to prevent shorts. I am assuming that the battery is bad because I have attempted to charge the unit, by leaving it on the track for several hours with the transformer set about 2/3 throttle, and also run the unit for several hours. - (At first, after being stored for a year, the engine wouldn't run at all, but it finally did take sufficient charge to get started.)
My question is: how do you get to the battery? Is it in the (heavier) drive unit, or the (lighter) rear unit. - Is it necessary to remove the entire upper housing of the unit? Frankly, this doesn't seem like a very convenient design, particularly since, as understood, if the battery goes dead and I try to run the unit I may foul up the memory, requiring that it be shipped back to the factory for a new circuit board.
Any suggestions will be appreciated. - Is there a way to turn the proto-sound system off so that I could run the unit without having to rely on the battery? (I have a 50-year old Lionel that doesn't give me any of these problems.)
Thanks, Jim
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Any suggestions? Jim
Jim Cate wrote:

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