I had one and it ruined every battery I used it one. So I'm hesitatant to get another.
What is meant by ruined—the battery wouldn't hold a charge, the battery's case cracked? What type of batteries were ruined—regular lead acid, AGM, GEL, lithium iron, lithium ion? In what range of air temperature was it charged?
The essential element in battery storage is that a battery within its functional service lifespan be
fully charged when it goes into prolonged storage (like off-season storage)—in frigid
or hot weather—regardless of whether it is to be stored simply with the battery ground cable disconnected from the transmission, or stored with its battery connected to a high-quality trickle charger. Using either technique, the battery should start the engine when the moto is eventually taken out of storage.
A slow charger, fast charger or trickle charger is unlikely to
restore a chronically discharged motorcycle battery.