The BN-V12U is a NiMh battery used in JVC video camera / recorders in the 1990s. It was used in a lot of competitors products, and found its way into other applications. In my case, it is used in a Leica T107 theodolite.
This article documents initial tests on two new after market Chinese made batteries purchased on Aliexpress 12/2023 for about $34 for two, incl shipping. These have a label rating them at 2.1Ah.
Defects
One of the batteries had a corroded terminal that prevented capacity testing due to its intermittent connection.
It was cleaned with a Burgeon 2834C fibre glass scratch brush (above), then cleaned with a lint free swap and IPA. The repair seems to have worked ok.
Test discharge
The capacity was measured for each of the batteries after two complete charge and discharge cycles, and then fully charged.
The discharge test is a 1A, approximately 0.5C. This might seem high for a NiMh battery, but they are often used in fast charge and discharge applications, and the original video recorder application was just that. They might deliver a little higher capacity on test at 0.1C.
Above, the discharge curves follow the classic shape for NiMh, and capacity to 1V per cell is 1.8Ah for each cell, 14% below specification. This is quite good, most Chinese batteries I have measured fall well below that, and there are articles on this site documenting 18650 cells of less than 10% of rated capacity.
Though lower than spec, the capacity is quite adequate, higher than the original batteries supplied by the Leica.
With luck and care, these may provide 5 years of service.