Who do you replace the batteries

I've never heard of a 1HD wheel chair and I've been at this for a long time. Assuming it's a Pride Heavy Duty (HD) then you would start by disconnecting the joystick from the base by unplugging it at the rear of the base, and cut any nylon cable ties holding the joystick cable in place to the base. Then remove the seat. Depending on the model, you can do this either with a lever on the side that unlocks the seat to allow it to pivot. If yours has this lever, unlock and turn the seat very slightly, then lift up with a **** with both hands and it should come off after a few good tugs...some need more coaxing. If the seat is a "post-mounted" seat, you will see it attached to the base with four posts at each corner and there should be a retaining ring holding the posts together. Remove the pins and lift the seat off(helps to have two people). It may have a rear locking seat where you release the front mechanism under the front of the seat and tilt the seat up, then slide the seat slightly forward and lift up. These are the only three ways I've seen a seat attached to a base. Once the seat is off, you need to remove the shroud covering the batteries. Many are simply held on with velcro, so if you don't see any screws holding the shroud on, just lift up on it and pull it away from the velcro. If there are screws, remove them to lift off the shroud. Now you will see the batteries. Disconnect both of them and move the wiring out of the way. Remove the front battery, then the rear, and replace with new batteries and reassemble. The seat and batteries are pretty heavy, so it is nice to have a helper.