Using motorbike batteries?

Since this is only for a school project, and since the goal is to only build a concept, could we use plain gel batteries laying on side, which would be like half price and way less dangerous ?

By connecting 3 motorbikes batteries together, i.e. about 10 kgs, I guess that we could have some “true” 36V for less than 300 euros eventhough that would last only 15 mn and would take the whole night to load…

What do you think ?

Heavy and very low discharge rate , not enough for me , you can get 2 lipo 20a 6s for 340€ … Or 3 16a 4s for 300€ …