Honda Minimoto 18V Sluggish With Weight

Hello All.. Great Forum.. I am learning alot.
I have already fixed on of the bikes I got with the help of this forum.
The other one I have I am still not having any luck.
It has good batteries and seems to spin just fine when the throttle is applied.
But when any weight is on the bike it just slows down to a stop. No Power at all.
I have tried to search the forum to find this issue because I am sure it has been addressed before but I am not having any luck.
I will be upgrading it later to 24v etc.. but right now I just want to make it go..

Thanks for the help!!

Tire pressure maybe.

The batteries are close to dead because they don't have the required amps to give the motor therefore it doesn't have enough "juice" to go with weight on it.

You would be surprised what a low tire can do on a 200 watt bike with a 200 pound rider. We're not talking about a 2hp gasser here. A flat can pretty much eat all of that 200 watts up. Don't ask how I know this..

Solution- air up and volt up!

But for sure it could also be the battery like he says.