How do you change batteries on hoveround mpv5 ?

It sounds like you have a failed right side motor.

Question edited for clarity.

Page 53 of the manual refers. When in doubt, it's a good read!

4 flashes: The right hand motor has a bad connection

https://www.hoveround.com/media/wysiwyg/pdf/MPV5-owners-manual-rev-U-0718_8-20-18.pdf..

..

SP12-35 NB (12 V 35 AH) batteries are available online, replace both at the same time.
link copy and paste
https://www.hoveround.com/media/wysiwyg/pdf/how-to-install-batteries-for-mpv5-mk3-power-chair.pdf

The larger batteries should have made them run for longer on a single charge. They aren't 35 amp batteries, they are 35 amp *hour*. 12 volts is the thing that matters. Check the batteries are correctly fitted and make sure the motors are clean. The fact they go down faster is puzzling and for that, I would exchange the batteries as they sound faulty.

Answer Edited for clarity. However, the motors are now the issue.

Easy to fit and easy to buy.

Hoveround MPV5 Wheelchair Batteries (Replacement)

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The Hoveround MPV5 wheelchair requires 2 batteries - SP12-35 NB (12 V 35 AH). Please note that you need to use all existing cables and hardware from your ...
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12V 35Ah SLA Battery Replacement for Hoveround MPV5

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Product details · ML35-12 SLA is a 12V 35AH Sealed Lead Acid (SLA) rechargeable maintenance free battery, Pack of 2 - UL Certified · Dimensions: 7.76 inches x ...
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Replacement Batteries for All Hoveround Power ...

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Hoveround · Hoveround MPV4 Power Wheelchair Replacement Battery (2 Batteries) · Hoveround MPV5 Power Wheelchair Replacement Battery (2 Batteries) · Hoveround ...

Hoveround MPV5 12V 35Ah Battery (2 Pack)

Raion Group https://www.raiongroup.com > hoveround-mpv5-12v-...

This Raion Power RG12350FP mobility scooter battery pack is a direct OEM replacement for your existing Hoveround MPV5 batteries (12V 35Ah).
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It could be charger issue or battery issue.
You can try this charger here: https://chargerbuy.com/products/charger-for-hoveround-mpv5-power-chair It's UL certified.

Here is te user manual to replace the battery where you can also find the fuse:

https://www.hoveround.com/Hoveround/media/Document-Library/how-to-install-batteries-for-mpv5-mk3-power-chair.pdf

The pressure is 50 PSI, but 45 PSI worked better for me.

The only thing to do is replace the battery.

If the power chair was stored for a while, the batteries may have gone bad. There is a gel inside them that needs to be put on a current regularly or it will solidify. When you connect the charger, you get a green light because it senses the batteries are full; unfortunately they are full of crud, not power. Try replacing the batteries to see if that solves the issue. You can probably take them to an auto parts store or Interstate Batteries to have them volt tested. The type of battery you need is a U1, 12volt, 33amp and you will need 2 of them.
Good luck!