DIY solar battery storage

[Berserkerboy]

I would like to retrofit the above.
I have a diy plug in solar system using microinverters which has been accepted by the DNO. I receive no feed in tariff and end up exporting energy for free once the solar diverter has heated our hot water.
Do I have to have an MCS installer to add battery storage for me? I have had quotes from installers but the price for the equipment is sometimes twice the price I would pay if I bought direct! Not to mention £400 for a few hours work.
Also, are batteries exempt from VAT after April 1st?