PRONTO M51 FEELS LIKE I AM DRIVING OVER ROUGH ROAD AFTER REPLACING THE BATTERIES. WHY?

Question edited for clarity, full 'make model (what it is)'.

Videos and where to buy.

https://www.google.com/search?q=m51+pronto%2C+replace+carbon+brushes

Service manual

Pronto Series M50 M51 M61 - PDF Free Download

http://docplayer.net > 58262751-Pronto-series-m50-m5...
Refer to Motor Testing on page 31 or Replacing Motor Brushes on page 116. Replace controller or send to Invacare for repair. Refer to Replacing the ...

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It means the battery voltage has dropped below the operating range of the chair electronics. Either need new batteries or maybe a charger and new batteries. There is always a chance of loose battery harness connections.

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Service Indicator Light Diagnostics - Invacare Pronto M51 ...

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Invacare Pronto M51 Base Manual Online: Service Indicator Light Diagnostics. ... Invacare power wheelchair owner's operator and maintenance manual.

The Pronto M51 takes two batteries. It takes what is called a U1 size battery.

The squealing noise is probably a bearing either in one of the four smaller tires called casters. The problem will not likely cause a break down right away but should be checked by someone mechanically inclined or trained in power wheelchairs. I don't know what you mean by the chair being "forced". Need more info.
May have something to do with batteries.

If the chair is driving slower and batteries are new their is a recall for that joystick from Invacare. Invacare is replacing joysticks for free.

Have you had the batteries load tested? How do you know the batteries are good?

recheck your polarity on the batteries carefully, i've done it for 15 years and the factory makes it complex sometime i connect backwards initially

why did you change the batteries, did you verify that it wasn't the charger in the first place, sometime the charger will appear to charge but actually isn't. put a meter on one battery then plug in charger if voltage goes up charger is good if not look for loose connections and or bad charger.

Have the batteries load tested. It sounds like the batteries need to be replaced.

Most likely you need new batteries. On the M51 powerchair the batteries are located in the center under the seat. Step 1 - remove the seat by pulling up on the swivel handle while lifting straight up, the seat weighs about 50 lbs. After removing the seat remove the center plastic cover by liting it off.
If you have an older model M51 the batteries will each have their own cover - to replace the batteries you will see several connectors that must be unplugged. The front and rear batteries each have different connectors so keep them separate. Lift out the batteries and follow the wiring for each replace the batteries. You will need 2 U1 batteries, available at sears or your local maedical equipment supply store ( Interstate has them too) Simply reverse the removal procedure to replace the batteries making sure you follow all the connections. - good luck
Tom