Welcome, from what I found on the web the Ransomes Diabline is an European cushman didn't find any pics.
Go with a lithium battery pack if possible. AGM is heavy lighter than FLA but still heaver than lithium based batteries. most 48V nominal LA based controllers can handle 14s NMC 51.8V nominal or 16S LiFePO4 51.2V nominal battery packs . I believe the motor should be abe to handle the slight increase in voltage. The weight reduction should help increase range, speed and payload capacity. I used an electric cushman garbage buggy at work close to 30years ago.
Later floyd
Go with a lithium battery pack if possible. AGM is heavy lighter than FLA but still heaver than lithium based batteries. most 48V nominal LA based controllers can handle 14s NMC 51.8V nominal or 16S LiFePO4 51.2V nominal battery packs . I believe the motor should be abe to handle the slight increase in voltage. The weight reduction should help increase range, speed and payload capacity. I used an electric cushman garbage buggy at work close to 30years ago.
Later floyd
