At charge currents << 1C NimH have a peak voltage under charge of about 1.4= 5 Volt, so 12V is JUST enough to charge 8. 8 x 1.45 =3D 11.6V,leaving you with 0.4 Volt headroom. Doable but close - a= s long as your nominal 12V is never lower than 12V. But if you want to fast charge (say 1C or more) then NimH needs about 1.7V/cell so you'd get 7 cells with about zero headroom - ie 6 or less in practice. 8 cells need > 1.7*8 =3D > 13.6V. If you are committed to 12V then 2 x 4 cell strings would be better. People frequently charge series strings, and there are ICs designed for this. It's not as good as dealing with individual cells as you need to do charge termination when the first cell is fully charged. You can do negative delta V end point detection, but as you increase string length then the % change if one cell hits end point alone decreases with cell count - so 8 cells giv= e 1/8th the endpoint delta V as a percentage. There are probably 8 cell chargers around but most seem to go up to 4. More certain charge termination at rates of 1C to 2C is achieved with delta temperature with absolute temperature as a backup. This can be one sensor per pack but better would be enough sensors to allow each cell to be checked for temperature. Some ICs include: This seems to do much of what you want. 2V to 20V battery. Switch mode for low heat NimH, NiCd , LiIon http://www.linear.com/pc/downloadDocument.do?navId=3DH0,C1,C1003,C1037,C107= 8,C1089,P1873,D1941 Also http://focus.ti.com/lit/ds/symlink/bq2000.pdf Up to 4 x NimH http://www.linear.com/pc/downloadDocument.do?navId=3DH0,C1,C1003,C1037,C107= 8,C1088,P7601,D5235 To get 20 Watt hours at 8 cells =3D 2.5 Wh/cell. Depends on load current. At higher currents with more cell drop you may get 1V/cell useable so mAh reqd =3D 2500 mAh. At 1.1 V/cell you need about 2250 mAh. My tests suggest that many/most cells do not meet their claimed mAh spec an= d even if they do, this drops off with age. Maybe at about 0.1% capacity reduction per cycle. So 20 Wh is pushing NimH over any time. An 18650 LiIon will give about 7 Wh. Depends on model and brand - maybe more. You can only charge 2 in series from 12V. (but 3 at 13V is doable. LiIon is very easy to charge control compared to NimH. Russell McMahon --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .