Lithium Battery’s

[dubob]

First comment,  you are WAY underpowered with a 80lb Terrova on a 21ft. boat.  You can never have enough power when you are using an electric motor.

Seriously,  look into upgrading your troller.  On a boat that size, you should be running a 110 lb thrust , 36 volt system!

No disrespect intended or implied.  But I suggest that this depends greatly on how the electric trolling motor is used.  I have a 24v PowerDrive 2 w/ I-Pilot (70 lb thrust) on my 19.5 ft ThunderJet.  In my case, I always push the boat and control the trolling speed with the 9.9hp kicker and use the electric trolling motor for steering only.  I have more than enough thrust in this scenario.  My 2 AGMs powering the electric motor will last 6 to 7 hours of constant 'ON' depending on wind conditions.  That's plenty of time to fish on any given day for this youngster.  If one uses the electric motor only for trolling, then I agree that a 100 lb plus trolling motor would be a better choice.  But the 70/80 lb thrust motors are adequate when used in conjunction with an outboard for propulsion for this size boat.

As to the battery type, I have been using AGMs for the last 15 or so years for my electric trolling motors.  They last me about 6 to 7 years which isn't too bad.  Lithium are definitely superior in every aspect except cost.  At 2 to 4 times more expensive than quality AGMs, I'll pass on the lithium.  If they ever get down in price to the $200 +/- $50 range, I'll consider the change.  If cost isn't a factor for you, then by all means go for the gusto and get the lithium's.