What is the difference between the NiMH battery type and the NiCD battery type???żżż

Chemistry, power density (capacity per ounce or per cubic inch of battery), power dissipation when not in use, lifetime based on # of charge discharge cycles.

The NiMh and NiCd nomenclature refer to the metals used in constructing the batteries. (you can look up the exact chemicals and metals for making the things...)

NiMh has a higher power density than NiCd. MUCH higner by the cubic inch measurement, not quite as high a difference by the weight measurement (NiMh cells weigh a bit more than NiCd per cubic inch) but there's still a considerable benefit in weight savings to get the same capacity.

NiMh tend to hold thier charge better while sitting on the shelf.

NiMh have a somewhat lower number of useful charge-discharge cycles than NiCd. the NiCd will seem to have suddenly gone bad (over 50% capacity loss in one cycle is typical. Trash/recycle them when this happens!). the NiMh (my resutls...) seem to drop in capacity "slowly" (dropping 10% capacity is the warning... just 5 or 6 more useful charges at decreasing capacity) when approaching end of useful life.

NiCD is reportedly able to release more electrical energy more quickly, than the Nimh. This would result as follows
NiCD would be used to highly power an electric flyer for aerobatics, needing all the power possible NOW, but
NiMH would release it over a longer period of time, as an electric flyer would want to power up to an altitude, then glide, then power up, then glide, or just fly around in lazy eights, or ovals, or touch and gos.

I know this is a rc airplane/beginers foarm but i have one of thows mini rc cars and I have two batterys for it, one Nicd and one NiMH and I want more power so I use the Nicd one.......right???żżż