The TCR101 was one of the first portable basic sonars. I seldom used it due to the cost of 6v lantern batteries that had to be purchased at the beginning of every season. $12 to $14 x2. Also have, nearly as old one of the early Ryobi 12V lithium rechargeable driver & flashlight.
Both being 12V, I gave it ago converting the TCR to lithium power.
L battery is 4 amp hr. & best I can find the TCR draws about 2. Sacrificed the flashlight as it was so redundant.
Heres the result. Everything fits nicely, even room for a spare battery.
