Interim Answer. {Awaiting reply from TDK support.}
[[TDK Life on Record Trek Max A34 Troubleshooting]]
SYMPTOM : max volume is available when plugged into wall, but only limited volume when running on battery.
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This symptom of going silent quickly when playing on battery at high volume did NOT occur when the device was brand new! [Bob]
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Sound mutes if it's turned higher than 3 lights. If it is connected to wall outlet it will play at max volume [rolis.kungs - 07/26/2017]
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Plays fine plugged into wall vol all the way up but if I run it off battery it will only go to about 3 full solid orange dots and then it shuts off. It will run for a long time off battery, but I have to keep it low. 3 dots or less. [Chris - 07/22/2018]
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I have tried the RESET procedure, and the fix was only temporary — the symptom of ‘going silent’ returned, same as before. [Bob]
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<TDK Trek Max A34>