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Rojza - tu masz po angielsku:

Conventional Ni-MH batteries employ a hydrogenabsorbing
alloy called AB5 type hydrogen absorbing
alloy for the negative electrode. This particular alloy
usually includes Co and Mn, as well as other soluble
elements in the alkaline electrolyte solution. These
elements dissolve into the electrolyte solution, and due
to their precipitation on the separator, the rate of
reduction of the positive electrode material accelerates.
1)
[2] Decomposition of the Positive Electrode:
At battery voltages over 1.23V (electrolytic
potential of H2O), the following oxidation reaction
occurs, which is responsible in part for the
decomposition of oxy-hydroxide:
NiOOH＋H2O＋ e- �� Ni(OH) 2+OH-
+) OH- �� 1/4O2+1/2H2O+e-
NiOOH＋1/2H2O �� Ni(OH) 2+1/4O2

[3] Self-Discharge due to Shuttle Effect:
Nitrogenous compound and other impurities
existing in the battery react which is called “shuttle
effect”, in which the nitrogenous compound goes back
and forth between the positive and negative electrodes.
In the following reactions, there is an electron ion
exchange between the positive and negative electrodes
which results in positive electrode reduction.
positive: NH4OH + 6NiOOH + OH- �� 6Ni(OH)2 + NO2-
negative: NO2- + MHx �� NH4OH + MHx-6 + OH-