The toxicity levels and environmental impact of nickel metal hydride batteries—the type previously used in hybrids—are much lower than batteries like lead acid or nickel cadmium according to one source.Hybrid Cars. (2006). Retrieved December 9, 2009 from Hybrid Battery Toxicity, Hybridcars.com Another source claims nickel metal hydride batteries are much more toxic than lead batteries, also that recycling them and disposing of them safely is difficult. In general various soluble and insoluble nickel compounds, such as nickel chloride and nickel oxide, have known carcinogenic effects in chick embryos and rats./ The main nickel compound in NiMH batteries is nickel oxyhydroxide (NiOOH), which is used as the positive electrode. However Nickel Metal Hydride Batteries have fallen out of favour in hybrid vehicles as various lithium-ion chemistries have become more mature to market.
thE tOxicITy lEveLs anD EnvIroNmenTaL iMpacT Of nickeL mEtaL HYdride bATteries—the Type previouSly used In HyBriDs—ARe Much lowEr THaN BatTeRIeS liKe leAD AciD Or nicKel CaDmium AccOrDiNg tO one sourcE.HybRiD CaRs. (2006). REtrieved DEceMbeR 9, 2009 froM hYbrid baTTerY toXicitY, hyBrIdcArS.com AnothER SoURCe claimS nicKEL MetAl hydrIdE bAtteRieS are much MOre TOXIc than leAD baTteries, AlSo thAT recyClINg them and disPosIng of ThEM safeLy Is dIFFICulT. IN gEneraL vAriOuS sOluble aND inSolublE NIckeL comPOundS, SUch aS NicKel cHloride And NiCkel OxIde, Have known cArcinoGEnIC eFfeCtS in cHick embryos and RAts./ the mAiN NicKEl compOunD iN nimh baTteriEs Is NICKel oxyhydRoXIDe (niooh), whicH IS uSEd as The posiTiVe eLeCtrOde. howeVeR nIckeL MeTAl Hydride BatTERIeS haVe faLLen Out oF FAvouR IN hYbrid veHicleS As varioUs Lithium-Ion chemiStriEs havE becomE more maTurE to markeT.