Been having this problem for a while now where when I turn the key in the ignition there is just a click sound, the engine doesn't turm over at all. At first after about 4 tries the engine would suddenly start and away I'd go, now it takes up to 10-20 tries before the engine will start

Then after doing my journey of about 10 miles when I needed to re-start it would go straight away at first, now it's doing the 10-20 times to start then as well.
When I've had flat batteries on previous cars, the engine would always try to start, albeit wioth not enough ooomph to fire before it did the click only noise.
Does this sound like the battery ?
On a side note so I don't get stuck anywhere I've seen a 3 in 1 re-chargable portable jumpstarter in a local shop for £25.00. It states the following:
battery type - re-chargeable sealed lead acid
Battery 12v 17ah
900 amp peak power
400amp boost power
Features
Inflation upto 260psi
12v dc output socket with overload protection
Charging level/battery condition indicator
400amp coloured cables
Rubber insulated 400amp booster clamp.
It's made by AM-Tech
Would it start the sedonna OK? It's a diesel 2.9 04 plate model