Hey Whicker, so I'm assuming that your unit starts up (albeit with the full check as you've described) then works but wont hold programs after you turn it off. I.e. dead battery. So you need a CR2032 lithium button battery with either the solder lugs attached or a battery holder which you solder to the PCB and insert a CR2032 into it. The battery holder (which is what you use to do the battery mod) needs to be the horizontal style and the solder lugs need to line up with the PCB holes (after you desolder the existing battery). You can get them from an electronics shop (Jaycar is the shop we use in Australia). It is also possible to get the CR2032 batteries with the solder lugs attached (similar to the one you'll remove).If you want to be certain, you can buy the mod kit (holder and battery) from MJMP (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm) 6 Euros + shipping. MJMP is in Belgium, he will ship to you, send him email from his web site or you can PM him on here. You can also buy the last (latest) EPROM from MJMP if you don't have it already (v2.01, it has additional factory presets and midi store/load to PC functionality) See attached pdf
After changing the battery you'll need to re-load the factory programs (from the EPROM (ROM) into internal memory):Press Store (it will light) then Hold Bank + 1 (display will read Presets Loaded)