Ultracapacitor smooths out the peaks and troughs of current in and out of the battery. Therefore, the maximum charge / discharge current of the battery is decreased. In this connection, the battery life is prolonged.
This technique was also applied to next generation EVs, for better energy recovery from regenerative brake.
Maxwell ultracapacitor
There are some 土炮as well
Who want to be a guinea pig to try this?
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Yes you are right. That device did able to prolong battery life (a bit)
But you usually need far higher capacitance to smooth out the big current especially during cranking.