Spotted this on hotukdeals..... am sure there's an argument for (and against) going third party battery but some may have preference to OEM.
https://www.amazon.co.uk/OM-SYSTEM-...&sr=8-3&ufe=INHOUSE_INSTALLMENTS:UK_IHI_5M_VF
https://www.amazon.co.uk/OM-SYSTEM-...&sr=8-3&ufe=INHOUSE_INSTALLMENTS:UK_IHI_5M_VF