1996 volvo 850 powered down, all panel lights came on, car died, generator not charging light had been on for a month (looks like a battery), what could be problem, is it expensive,

FUSE PANEL LOCATION
The fuse panel is located in the engine compartment. A label on the inside of the cover lists the fuse amperage and circuits protected.
volvo 850 fuses fuse panel layout service repair manual
FUSE PANEL IDENTIFICATION
Fig. 1: Fuse Panel Identification
Courtesy of Volvo Cars of North America.
WARNING: Always disconnect battery ground cable before servicing "high-current fuses. It is recommended that "high-current" fuses be replaced by a qualified technician.
* 1 - 15 Amp
Fuel Injection, Distributor Ignition, Automatic Gearbox
* 2 - 15 Amp
Fuel Pump, Alarm System
* 3 - 10 Amp
Courtesy Lights, Oil Level Sensor
* 4 - Not Used (1993-95)
* 4 - 10 Amp (1996)
Electronic Start Inhibitor (Immobilizer)
* 5 - 30 Amp
ECC Blower (Speed 4)
* 6 - 25 Amp
Central Locking System, Alarm
* 7 - 15 Amp
Audio System (Amplifier)
* 8 - 25 Amp (1993-95)
Power Antenna, Trailer Connector
* 8 - 40 Amp (1996)
Electronic Start Inhibitor (Immobilizer)
* 9 - 30 Amp
ABS, Traction Control System
* 10 - Not Used (1993-95)
* 10 - 15 Amp (1996)
Heated Rear Seat (If Equipped)
* 11 - 30 Amp
Heated Rear Window & Side Mirrors
* 12 - 10 Amp
Brake Lights
* 13 - 15 Amp
Hazard Flashers, Headlight Flashers, Alarm
* 14 - 30 Amp
ABS, Traction Control System
* 15 - 10 Amp (1993-95)
Audio System, Courtesy Lights, Door Open Light, Trunk Light, Glove Box Light, Remote Control Central Locking System,
Oil Level Sensor, Seat Belt Reminder
* 15 - 10 Amp (1996)
Audio System, Courtesy Lights, Door Open Light, Trunk Light, Glove Box Light, Remote Control Central Locking System,
Oil Level Sensor, Seat Belt Reminder, Data Link Connector
* 16 - 30 Amp (1993-95) Accessories
* 16 - 30 Amp (1996)
Power Antenna, Trailer Connector, Accessories
* 17 - 10 Amp
Key Reminder
* 18 - 25 Amp (1993-95)
Heated Front Seats, Power Mirrors
* 18 - 15 Amp (1996) Front Fog Lamps
* 19 - 15 Amp
Left High Beam Headlight
* 20 - 15 Amp
Right High Beam Headlight, High Beam Indicator
* 21 - 15 Amp
Left Low Beam Headlight
* 22 - 15 Amp
Right Low Beam Headlight
* 23 - 10 Amp
Left Parking Light, License Light
* 24 - 10 Amp
Right Parking Light, Bulb Failure Warning Sensor
* 25 - 10 Amp
Rear Fog Lamps, Fog Lamp Indicator
* 26 - Not Used (1993-95)
* 26 - 25 Amp (1996)
Heated Front Seats, Power Mirrors
* 27 - 15 Amp
Back-Up Lights, Turn Signals
* 28 - 10 Amp
Cruise Control, Heated Rear Window, Seat Belt Reminder Light, Shiftlock, Bulb Failure Warning Sensor, Heated Rear Seat
* 29 - 15 Amp
ABS, Traction Control System
* 30 - 10 Amp
Cigarette Lighter
* 31 - 25 Amp
ECC, ECC Blower (Speeds 1-3)
* 32 - 10 Amp
Audio System, Remote Controlled Central Locking System
* 33 - 15 Amp (1993-95)
Power Seats, OBD Test Socket, Tailgate Washer/Wipe (Wagon)
* 33 - 15 Amp (1996)
Power Seats, Tailgate Washer/Wipe (Wagon)
* 34 - 25 Amp
Windshield Wiper/Washer, Horn, Headlight Washer/Wiper
* 35 - 10 Amp
Instrument Lights, Sun Roof, Traction Control System
* 36 - Not Used
* 37 - Circuit Breaker
Power Windows, Power Sun Roof
* 38 - Not Used
* 39 - Circuit Breaker
Drivers Power Seat
* 40 - Circuit Breaker
Passengers Power Seat
RELAY PANEL LOCATION
The relay panel is located at the left corner of the instrument panel.
i copied this off a volvo site Hope this helps

You may have a bad positive battery cable, with a digital volt meter you can test and see if you are getting 12 volts through the entire cable or at least to the cable junction block, in or by fuse relay center, then check cable from there to starter. you should also check the main, battery, power, fuses and relays, usually in the under hood relay center(fuse box)
Car Repair Maintenance How to Check if Relay Is Bad

#1. Check the secondary cable which runs to your starter.
#2. Check Starter Relay (unplug, and shake it - sometimes to can hear broken stuff inside of them)
#3. Make sure your cables are tight, and your battery has a good charge. (was it trickle charged ? jumping and then turning the car off will not be enough charge for the battery ; you must charge to 100%)
#4. Check all grounds.

Check that your rear interior lights shut off. Other than that disconnect the + Battery cable and put a voltage meter between the two. Pull all of your Fuses and replace one at a time checking to see if the voltage changes, this will show you where your problem is.

Need to check the dash light dimmer switch first. You need to remove and access the switch and check for power to and thru the switch. It controls all the panel lights for the dash.

there is a head lamp switch mounted to the steering column. it has died. to access it you have to remove the cover under the dash. remove the four bolts hold the steering column and let it drop down. find the switch usually behind and to the side of the ignition switch. there will be a rod giong to it from the handle. remove and replace the switch and assemble in reverse order

well the first thing is to have the battery and charging system checked,this will cause problems if battery isnt fully charged at all time.the next thing is it started running bad after a car wash, this tells me you may need a tune up, may have bad plug wires, the best thing to do first is have the computer scaned and see what codes are stored in there, this will give you a generally idea of the problem or where to start. autozone scans for free. hope this helps.

First thing to look for as a current drain is the glove box light. The switch will slowly move into the dash allowing the light to stay on. This is quite common to the 850's

It's in the console under the coin holder, in front of the gear shifter. You have to remove the coin holder and you will see it.

I would check that the auxilliary drive belt that runs the alternator and probably the water pump hasn't just broken, causing the engine to overheat and the battery to run flat. Just a suggestion, hope it helps.