battery questions for electric trolling motor

[Vanmel]

Hi guys, hope I am on the right section of the forum...
I just bought a trolling motor for my inflatable boat, it is rated 45 lb and according to the seller (bought from ebay), it has battery req of 12v34ah

I have an unused 12v 38AH (VRLA) battery but not too sure if it is deep cycle or not (don't even understand what does deep cycle refer to..)
From what I gathered from google and especially minn-kota website, they recommend to get 85 ah battery minimum ?!
Checked on their price, its not cheap

I bought that trolling motor with a thought that I could use the extra battery I got so, any thought about this?
Should I try using this battery ? I wont be going far with the inflatable boat, max 1 hour total. We re just going for squid fishing around Tootgarook boat ramp to rye pier the furthest. Infla boat size is around 2 mtr, 400 kg rating boat.
Would it affect the motor performance? Damage it? Damage the battery?

Thanks in advance.

[purple5ive]

You won't get much life out of it. That's all.
Higher rating oh AH will give you lonfer time on the water.

[Vanmel]

You won't get much life out of it. That's all.
Higher rating oh AH will give you lonfer time on the water.

Thanks mate, how long you reckon 38ah will last for ? As I pointed out, we would only use 1 hour max in total motor usage. (will use oars for short distance)

[purple5ive]

all depends on how much juice the motor uses mate, if you are on full pelt and say it uses 10amps then you have 3 hours before it runs out.
only way to find out is to use it first i guess.
does your trolling motor specs say anything about current draw??

[re-tyred]

A quick google of 45lb electric motors shows that they use around 400 watts. So approx. 4amps. A 38ah battery can deliver maybe 20aH in practice so approx. 5hrs in theory. In practice if the battery is old it may not deliver even that.
Deep cycle batteries deliver a larger amount of their rated power before the voltage drops too low. Deep cycle are suited to long slow discharge and then a long recharge. High crank batteries are used in vehicles to supply large current when starting. They are then recharged quickly by the alternator on the motor. They will drop to a low voltage quicker.

[skronkman]

A quick google of 45lb electric motors shows that they use around 400 watts. So approx. 4amps. A 38ah battery can deliver maybe 20aH in practice so approx. 5hrs in theory. In practice if the battery is old it may not deliver even that.
Deep cycle batteries deliver a larger amount of their rated power before the voltage drops too low. Deep cycle are suited to long slow discharge and then a long recharge. High crank batteries are used in vehicles to supply large current when starting. They are then recharged quickly by the alternator on the motor. They will drop to a low voltage quicker.

If it's 400 watts then the equation is amps=watts / volts = 400 / 12 = 33.3amps. Which is approximately an hour in theory and much less in practice on a 38ah battery. For the size of the battery (38ah) 33amps is a much higher discharge rate than what it is spec'd at (usually the 20 hour rate (about 1.5amps), you are running it closer to the 30 minute rate) at so you can expect a shorter run time and short battery life if continually used in this way.

If I had to hazard a guess I would say that you will get about 25 mins of motoring which leaves very little contingency or leeway in the case that the battery is getting old, not charged properly, etc.

[4liters]

Look at the amount of amps it will draw and think about how many hours you'll be using it in a session. Multiply the two and that'll tell you the size battery you need. If it's your only means of propulsion you might consider over estimating the time you think you'll spend on the water so you always have some juice in reserve in case you have to come back in against the wind or current or something. Think about what sort of fishing you're doing too, driving to your mark and spending 8 hours at anchor will clearly use less power than 8 hours of trolling.


As Re-Tyred says, make sure it's a deep cycle and not just a car battery. Be careful with Li batteries because a some motors haven't been tested properly with them. It's probably worth buying a decent battery even if it costs more because if it's your only motor you're up **** creek if the battery dies

A quick google of 45lb electric motors shows that they use around 400 watts. So approx. 4amps. A 38ah battery can deliver maybe 20aH in practice so approx. 5hrs in theory. In practice if the battery is old it may not deliver even that.

I don't think that's right. For example a 44lb Watersnake will draw about 40 amps on max power

[re-tyred]

My maths were wrong it was 5am lol I was rounding it out in my head but did it for 40watts not 400.

[Westfish]

I run 125 amp hour deep cycle batteries for my 55lb bow mount.
Should get all day in most conditions.
I did have 2 batteries for trips away to make sure I had plenty.
If your planning on trolling all day with it you would be pushing the limits.

[gregmaka]

Keep in mind you still require a boat licence and all safety gear,water police are everywhere.