Battery swollen. Mainboard damaged? Tablet-Phone battery swap?

I have an old tablet with a swollen battery. I’ve disposed of it but it didn’t say what the voltage was. The device has “5V, 2000mA” on the back. I’m not sure if this is referring to the battery output or input?

I have connected a battery from another Android device with 3.85v and 4.40v on the back. A multimeter shows 4v.

When I try to hold the wires onto the terminals and turn the tablet on, nothing happens.

Could this because:

1) The battery is the wrong voltage

2) I’m just struggling to hold the wires on the battery terminals properly

3) The mainboard is damaged?

Thanks!!!

p.s. How can I safely use an mobile phone battery in this tablet without soldering? Is there some sort of clip I can buy or make for connecting to the battery terminals safely?