Just applied for a zero interest on purchases credit card so the current plan is to get the battery and invertor myself on the credit card, 21 months to pay, sorted
Whils’t this seems like good idea and is on the supply cost basis, there are also pitfalls that may out weigh any positives.
If it is faulty you will have to arrange replacemen, with the risk of paying for the installers time on the premises upto determing the unit is faulty.
If the installer warranties the install and something went wrong with the unit 6-12 months down the line, you would probably have source a replacement part by doing a warranty claim and the installer could charge a fee for diagnosing the fault and fitting the replacement part, something that may have been otherwise included by the installer.
Something for you to think about.