[Duncan]

Hi
The AC 51 sounds far too small for that machine - expensive AND wimpy

I would look at a new battery pack - Volt or Leaf modules and just try to get the rest working

Losing about 1000 lbs + all of the watering gubbins may make the thing go quite well enough with its present power unit

 

[Duncan]

Hi
The charger and the controller are usually separate units - even if they are in the same box they don't share much

Motor/controller efficiencies are all pretty similar - I would be surprised if you could measure the difference!

If you really wanted to replace the motor then I would look at Leaf or Tesla parts
Both will be a lot more powerful than the AC 51 - for the same or less money

The best thing to do is to get "Tore in" and take your existing machine apart and look at the bits

The battery is a throwaway (try and sell it - may be useful for a house solar set-up) - no matter what you do it's not going back in - as is all of the watering system
The old charger is also a throwaway

The rest of the bits may not be up to date but they will not be horribly out of date and will be quite useable

If the motor controller (Not the charger) is buggered THEN it may be worth changing it all out - but it's worth trying to fix it
A properly cooled 8 brush DC motor is very sensible technology and probably BETTER than the AC51