Welcome to the Pool Opeth8
If you were talking about an older vehicle I'd say the Fault lies in the Solenoid this is where the "+" battery cable goes to the starter or it goes to a intemediate relay with 2 thick battery cables and 2 or 3 thinner cables
You should have a rubber cap on this terminal If its the older type there are 2 rubber caps yes? Latest versions are either mounted Piggy back on the starter or are built in?
I assume you have not done a Starter solonoid test before?
Do this when it is difficult to start
Get an Insulated screwdriver (Largest Old one will do wooden handled OK) lift both the rubber caps exposing the terminals beneath switch the ignition ON Now bridge the 2 terminals for a second or 2 with the screwdriver shaft
only You'll get a Big blue welding type spark
Your engine should now start?
Warning If you go more than a second or 2 the screwdriver will try and weld itself with the High amperage!!
If the engine starts then the solonoid wants attention if part of the starter? Has to be taken to an Auto electricians for repair
They do an exchange scheme in the UK you bring your old starter in and you pay for a guaranteed
reconditioned replacment
They only repair if there is no replacement (more expensive) option 3 is a brand new unit (avoid unless you have a deep pocket)
Vehicle breakers will carry stocks though there is no guarantee it will work (no refunds) though some do give it a test in front of you if you ask nicely
If you have a separate solonoid then the best option is to get 1 from the breakers they don't sell reconditioned only New
