Bundeenabuoy said..
Currently my Swanson 28 (3.5T) has a windless with 5/16 stainless steel chain and a dsl anchor.
Can I try to attach a electric motor to the windless or should I replace it with a new electric winch?
I have one starting battery and two house batteries.
What would you recommend?
Not sure what a "dsl" anchor is, the chain should be good to go and the windlass I am guessing is a manual. The previous owner put lots of nm"s on the boat with anchoring the norm so I would suggest learning to use what you have for a while and then making decisions re upgrades. This strategy will show where and if any deficiencies lie and enable you to correct them without making costly mistakes, (don't ask how I know

)
If you feel the need to upgrade the anchor you will need to decide weather you want a shovel type or a plough style, and assess the various offerings.
Cheers, Bob.