I fully charge my batteries with the external Canon charger. When I check them with multimeter, they show a full 8V charge. When I put in camcorder, however, they drain in about 2-3 minutes. Then when I check the "dead" battery with multimeter again, it still shows a full 8V charge! What's going on???
Voltage and Amps are not a measurement of capacity.
A multimeter can only tell you what the battery's nominal voltage or amps is when measured, not for how long that voltage or amps can be sustained or delivered.
No one can say conclusively what the problem is.
Its possible your charger might not be charging the batteries
The batteries (if all the same age) and older might be failing (but all at the same time is unlikely)
Your camera could also be to blame, hardware issue, something malfuctioning causing the power to drain in a short period of time.
It is 12 yrs old, so its possible that any one of these items might be to blame.
Bay Area - CA
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It basically happened with four different old batteries: external charger indicates battery is fully charged, measurement on multimeter says 8V, put it in camcorder and roll camera - the battery charge icon on the camcorder screen rapidly drops down (within 3-6 minutes) until it dies...
I checked all contacts for corrosion. None...