Thinkpad 700 not starting up

[hosseino]

My old thinkpad 700 (9552-300) that I bought in 1992 is not starting up. It hadnt been started for a few years while it was in storage at my parents. (My parents also threw out the power brick when they moved last year, but i was able to buy another one). The main battery does not charge, however the charging light is on on the laptop. However that main battery has been dead for years and i was able run the laptop just off AC power before it went into storage a couple of years ago. I'm suspecting the issue is with the "standby" battery as opposed to the CMOS battery because i dont think a dead CMOS battery would prevent it from starting up.
When i turn on the power switch, the laptop makes a very slight click/whirr and the AC power and battery charging lights go out immediately. Turn off the power switch and the two lights come back.

Any other suggestions besides the standby battery (part 44g3779)? I ruled out the internal voltage converter because I understand that a faulty voltage converter would only be a problem for running off the main battery.

BTW - as of 2013/2014 when i last powered this thinkpad up, the CMOS battery was still powering the date and time correctly after 20 years.

[fultontech]

My P75 turned on until a couple of months ago. But with that, it's a known issue. Failing Capacitors. Perhaps it's something similar that will require a soldering iron and multimeter.