FES underpowered for 18m ship?

I just had a chat with a fellow pilot whose friend sold his LAK 17b FES because he was disappointed by the ability of the FES to gain altitude. The problem being that when applying sufficient power to gain altitude, the battery would get warm to the point where the controller shuts the motor down. I read recently an accident report tied to the same issue, in that case pilot too low and not in reach of a landing spot (pilot mistake) who counted on FES to regain altitude, but as the battery was too hot it wouldn’t power the motor and the pilot crashed. On the other hand FES works reliably to maintain level flight at a lower power ratio.

Does any LAK 17 or Shark 304 FES (or other glider of similar weight) pilot have any feedback on this? In real life, how much altitude are you able to gain, with fresh and semi full batteries? Is it a matter of being patient and accepting a low rate of climb?

It would be disappointing if when you fly “by the rules� and remain above a landing / outlanding spot until you turn power on, that the FES doesn’t allow to regain altitude, but only to maintain level flight. It changes the flight planning strategy altogether.

I find this surprising and I’ll try to get in touch with the pilot who sold his LAK, but thought I would ask the question in the forum in the meantime.