The battery tester showed only 9.8-10V on what's a 12V battery. The only thing that casts doubt is that it wouldn't start with a battery charger on 'start' mode.
Lots of newish cars won't even try to start if the battery voltage is much below 12v, as the current draw and voltage drop could cause damage.
If your battery is that flat, a booster pack will struggle if all its power is trying to charge a very dead battery.
Disconnect your battery - ve and cover the battery terminal so it can't touch again. Use a set of jump leads from another good battery/car, or booster.
Key from off to run NOT START. Do the dashboard lights look normal. Glow plug light goes out if it's a diesel.
If it looks good and your jump leads are heavy duty, or your booster is rated for cracking an engine as opposed to assisting, you could try starting it.
Alternatively, charge your battery before reconnecting the -ve and trying to start the car.
If disconnecting the battery for an hour didn't work. I doubt that overnight would be any different unless the battery is on charge overnight and holds about 12.8v after you switch off the charger.