Had about 11 Volvos since the 70s. Never had this trouble before. Now have a 1998 V70 Estate with less than 100k on the clock. Battery kept going flat unless driven within the previous 48-72 hours. New battery fitted last Sept or so. No improvement and getting worse. Now battery flat after 24 hours. Been to 2 different garages both flummoxed as to where there is an electrical leak. All switches off, boot door securely down. Only modification is a reversing camera installed before I got the car. Tried an OBD II vehicle fault code reader - no fault observed.
Has anyone got a bright idea as to where the hidden leak might be?

 

The svxc70 98-00 - get bad connections inside the positive battery cable and the B+ wire going to the fuse box under the hood. That high resistance connection prevents the alternator from charging and the car from starting erratically. Where the cable is crimped into the battery terminal. After the car has fun for a while check the temp of the terminal - careful they can get hot enough to burn your finger. Also the B+ wire - the 4 wires connected to the bolt on the positive terminal. They go the to bolt in the fuse box under the hood. Loosen that nut and pull the wires up looking for melted wires where crimped into the ring terminal.

Best diagnostic tool for both of those is a voltage drop test. Volt ohmmeter lead on the battery, other on the alternator output or other positive source, with circuit under load, that is the engine running (yes positive to positive). In theory the voltage should be 0 - any more than .2-.3 volt - there is resistance in a connection.

If all that checks use an inductive ammeter to see if something is turned on. Some of those cars have the glove box latch in the middle and the glove box light switch in one corner at the top - the glove box door warps and the glove box light stays on all the time - Don't remember if the 98-00 had that design. But many battery drains where fixed by removing the glove box light bulb.