My DeWault charger DE9107 does not charge battery pack.Output voltage is 0

I'm far from a Roomba expert and only clicked on your question out of curiosity given my background and as there was a similar question earlier Id passed.

A little research... Roomba NiMh battery pack is 14.4 v full charge. NiMh charging is a bit complicated, suffice to say it will eventually go well over 16V.

I would expect the charging station to have an initial charge voltage in excess of 12.5V. What I don't know is if its always on or waits to see if a load (roomba) attaches and then turns on its output.

So if you measured the power, contacts on the charger with a voltmeter and you get better than 12V likely its good, but really need to know what the voltage is when Roomba (with nominal battery pack) is docked.

Its likely the battery pack in the Roomba has a bad cell and will need replaced. You could measure the battery voltage but likely its low from not taking a charge. If its 14+ then the charger is working and the Roomba is misreporting.

First thing to do would be to check the voltage output of the charger to ascertain if it is working properly. The voltage out of the charger should be higher than the battery pack voltage. Next (if you have the instruments) check to see if current going through the battery pack. If you have no current flow and still have the correct voltage then one of your cells is either faulty or the pack has open circuit wiring or has been repacked incorrectly.

No make and model # makes answering difficult so I'll have to give very general information. Also I'm assuming this is well out of warranty - otherwise call the manufacturer first. Now, when we start without any schematic we trace backwards from where we know the circuit should end. In this case you start at the battery terminals since you're trying to find the charging circuit. It is more difficult today since if there's a microprocessor in the mix it could be controlling when a given line is active, when the charging line is connected to the battery, or not. The charging circuit will be a constant-voltage circuit for Li-Ion batteries ~ 3.7 Volts depending on the battery. If it is Lead-Acid it will probably be 13.8 - 14.0 volts, if Ni-Cd or Ni-MHd then it depends on the size of the battery pack and again will probably be a max voltage of about 1.25V/cell * Number-cells. Once you find the circuit you can test to see if there is any output voltage and current when it is "on" - if it never turns on then the problem is either the circuit is dead or the CPU is not turning it on - if the CPU controls this. If you can find the line from the CPU to the charging circuit see if it ever changes state, if not you could try "forcing" a different state, ie, it the state is always off (usually a 0 Voltage) then try finding the voltage line to the CPU and place that voltage on the CPU to Charger circuit line. If the line is always high (anything from 3.3 V to probably 5V depending on the CPU's power requirement) then try lowering the voltage to a 0 state. This is much more difficult since it may require cutting the line from the CPU to the charger. If either of these gets the charger to work then the problem is with the CPU, if nothing gets the charger to work the problem is the charger.

battery pack already exhausted or your charger is defective, check your charger by using voltmeter, if there is voltage output more than your battery voltage that means your battery needs replacement.

PLEASE NOTE: The Low Voltage Protection feature on this battery charger will not allow the charger to activate unless it is connected to a battery pack that has a minimum voltage of 16 volts. Battery packs with voltages below that level of charge cannot be recovered or recharged. This is a safety feature to prevent overheating in the event of a faulty battery. This battery charger will not output any voltage to the XLR connector until connected to a battery pack meeting this minimum voltage requirement.

Check the charger output, it should be about 4-5 volts higher than the battery pack voltage rating. If the charger voltage output checks ok then the battery pack is defective. Any Radio Shack store can test the charger for you.

Probably the battery pack is worn out or has a "memory" problem. A worn out pack will have one or more cells shorted internally (one or more cells read 0 Volts, and an ohmmeter reads less than 1 Ohm when connected to the 0 Volt cell). If it is a memory problem, it is possible to recondition it, but not simple. You have to remove the pack, then connect a 150 Ohm resistor across each cell and let the battery sit until the cells are completely discharged. You can't just connect a resistor across the entire battery pack because the stronger cells will reverse-charge the weaker ones, which will cause them to short out.

Running the battery too far down will cause the reverse-charge problem, but not running it down at least occasionally will cause the memory problem. (Memory problem explained: the cadmium crystals grow when the battery is charged and shrink as it is discharged. However, the larger ones tend to remain intact on discharge and grow faster than the smaller ones. Eventually they block the ion flow through the battery, so the battery loses capacity. It's called a memory effect because the battery only "remembers" it has the capacity to go down as far as it is habitually used. Running the cell all the way down dissolves the over-sized crystals.)

It is possible you have a problem with the charger. Check for voltage on the charger plug. It should be about the rated output voltage printed on the charger box before messing with the battery.

at a guess i would say about 16 volts

Measure the output voltage, if it is low then you must replace the charger, they don't sell parts to repair them.