Because NiZn appears to hold more kwh per pound of battery and advertises more cycles per battery. The MB80's I bought
at $270 each weigh ~36.4 pounds. Nameplate rating is for 64 Amp Hours. (see: http://www.evercel.com/manufacturing.html
) The Optima Yellow Tops I purchased here in Connecticut were $189 less a core charge of $10. The
YT's have a nameplate rating of 55 Amp Hours at the c/20 rate and the spec sheet says they weigh 43.8 pounds.
A discharge cycle graph on my battery cycler show what we've got:
The purple line shows that the battery delivered about 70AmpHours down to the recommended
cut off of 9.6volts. The yellow line shows a ~20amp discharge rate. The dark blue line shows the case temp getting
up to about 35 dgrees C, but cooling down quickly after the discharge stopped.
I like getting more than the nameplate out of a battery. I like having almost
1kwh in this small package!