Battery changed / voltage on battery same across switch / non functioning completely dead

TS-1 Revision 4.3

Changed battery; nothing. Test replacement and original battery for voltage both test good. Voltage appears same at switch solder points on board of unit that will not power on, unit will not go into charge with flashing light, unit is dead despite voltage on switch. Switch is operable, clicks nice and board is clean, no signs of any damage.

Not sure how far to go in to testing as I have a replacement battery already and little knowledge of circuit path. Is there a simple multimeter test you would recommend next?