I don't think it works that way. And with the battery charging to 29.7 after a full charge it's clear something is not right. Now some chargers need to be a tad over to fully charge a battery. But this does not seem to be the case here.
It is important to keep the individual cells from being charged over their 4.2 volt maximum capacity. Damage or fire could result.
What I think we know...
1) The controller is keeping the motor from running above 29 volts. (controller high voltage limit)
2) The battery states it's operating voltage is 20 to 29 volts.
3) You have a charger that is rated
at 29.4 vdc but over charges
to 29.7 volts.
What to do? Possibilities...
1) Have a talk with the seller to make sure you have the correct parts
, verify battery cell construction and type
. Possible replacement of charger. Get correct parts.
2) Just manually
charge to 29 volts or where the motor works, that is at or under 29.4 volts for a 7S battery. (verify)
3) Add a correctly sized diode in the charging circuit which would reduce the output of the charger by .7 volts.
4) Open up charger and see if it is adjustable.
Now charging short of the batteries full capacity all the time may cause the cells to become unbalanced over time. Which will result in a loss of capacity if they do...