amp I bought 3 days ago not powering on - electrical engineer advice wanted

This is the battery you need, $22.95. Last one available in USA. 

https://www.ebay.com/itm/185748089723

I am sure your tech is on it. 

@parkergetdean ,

For posterity; What make and model amp is it that you own and that your tech is allegedly working on???!

nice!

@goodlistening64 he said he paid 50 for it

I am very fortunate to have a local tech that I trust and find quite reasonably priced. He was recommended to me years ago by another poster here. When Kris is done, he contacts me. Creating a time constraint for a tech is not something I would do.

@parkergetdean 

Probably be a good idea to get a backup battery since you know it is going to fail! Can't even guarantee there will be any left in five years or so..

If your tech told you what he paid, that is a good sign! Not a bad time to tell him it may not have been serviced in some time and a cleaning/lubrication may be in order. 

If it's already on the bench, he may do it for $100 or less...and it may sound better because of it.