Reputedly the 1961 Power Punch battery had color-coded plastic caps.
Red caps = standard issue 55 amp hour battery.
Gray caps = the 65 amp hour battery.
Yellow caps = the 70 amp hour battery.
Would suspect that the 55 amp hour battery is for the '61s w/o power options or air conditioning.
The gray cap model for vehicles with some power accessories.
The yellow cap model for vehicles with all the bells and whistles.