Unexplained switch to RTL Mode

Can someone identify why my plane switched to RTL Mode?
I was flying around line of sight in Manual, when the plane started fighting me and acting very strange. It took me a while to identify what had happened.
The logs don’t show that I selected RTL. The only mode used in this flight were Manual (2200) and FBWA (988)
I never had a failsafe event.

It occurs at 63% on the attached tlog.

APM 2.5.2
Plane 3.02
Twinstar II
Airspeed sensor

Post the .log from APM, the answer is there.

.log attached
Where do you recommend I start looking? I can see the RTL in the .log, but not what caused it.

Thank you

line :
25297 - low battery 10
25298 mode RTL 11

You did not log PM, or Throttle/RC - so I can’t say - but you’ve been climbing for a while before, and climbed during the event, so it’s most likely battery voltage that dipped below.
The speed was increasing during the climb, so your throttle must have been high.

[quote=“Andre-K”]line :
25297 - low battery 10
25298 mode RTL 11

You did not log PM, or Throttle/RC - so I can’t say - but you’ve been climbing for a while before, and climbed during the event, so it’s most likely battery voltage that dipped below.
The speed was increasing during the climb, so your throttle must have been high.[/quote]

Thank you Andre.
I did not realize that the FS_BATT was set. I never use battery failsafe, and I don’t know how I missed this. Sorry for not figuring this one out myself.