Picked up a cheap Fluke AC/DC differential voltmeter, model 887AB/AN, at a hamfest this past weekend that's acting a little flakey. When it's switched to battery operation, the meter deflects full scale and remains that way until switched off. Any ideas? Is this a typical failure with these? I haven't attempted to connect a power cord to it yet since it has a few disconnected wires coming from the area where the transformer, AC plug, etc. is and I haven't obtained a schematic, calibration info., etc. for it yet.
The battery pack is said to be good, and I was told that it should be charged once every week or two... not sure for how long though; will the batteries be overcharged if charged for too long?