11-13-2022, 11:35 AM
With NiMH AA cells, there's no real danger of explosion or fire unless you dead-short a fully charged cell, they're not as touchy as Li cells.
Old cells might leak, don't bother with cells that have white or greenish crud on them near the seal (+ end), these should be disposed of safely.
The simple way to find out if an old NiMH cell is still good is to put it in a smart charger. Such chargers can sense and reject bad cells.
One problem that a smart charger can't detect is excessive self-discharge, which would drain the cell in a few weeks. The solution is to let your charged set sit on the shelf for a few weeks and put them in the charger again. The charger will tell you the state of charge of each cell, either directly or by the time it takes before the charger signals "charging complete". Good cells can hold their charge for months.
One problem that old cells invariably suffer is tarnished contacts. This is easily fixed by a gentle pass with a fine wire brush. It is essential that the contact be nice and shiny, even a slight tarnish will render an otherwise good cell useless.
Old cells might leak, don't bother with cells that have white or greenish crud on them near the seal (+ end), these should be disposed of safely.
The simple way to find out if an old NiMH cell is still good is to put it in a smart charger. Such chargers can sense and reject bad cells.
One problem that a smart charger can't detect is excessive self-discharge, which would drain the cell in a few weeks. The solution is to let your charged set sit on the shelf for a few weeks and put them in the charger again. The charger will tell you the state of charge of each cell, either directly or by the time it takes before the charger signals "charging complete". Good cells can hold their charge for months.
One problem that old cells invariably suffer is tarnished contacts. This is easily fixed by a gentle pass with a fine wire brush. It is essential that the contact be nice and shiny, even a slight tarnish will render an otherwise good cell useless.