Thread: Battery power consumption question

I've got a MK Max 74 and 2 Group 27s to power it. My boat (aluminum) will cut about 1.8 to 2.0 mph at 40% with it. The question is, how long should I expect to be able to maintain that speed on constant before the batteries give up.

I kind of know the answer already - about 2 - 2.5 hours with my current batteries, but I'm wondering how long I could expect out of a fresh set of batteries. Mine are about 1 year old now, but truth be told, they are mismatched as I added the second after I bought the boat.


Group 31s are not an option for me unless I mount them somwhere other than the back.


Wannabe...

There are too many unknown variables to compute. For instance, how many amps does the motor draw at 40% keeping in mind its not linear? The condition of the batteries, (group 27 are rated at 85-105 amps). Then you have to consider that your motor has a maximizer. When running wide open it basically does nothing, but at 40%, how much current does it save you? Useing guestimates like saying the motor draws 20 amps at 40%, I come up with the same you do, 2-2½ hours. Maybe Canepole can shed some better info on this.

Ibn, you kind of sound like you know what you're talking about. That being the case, what are you doing hanging out here? LOL.

Anyway to measure the draw at a given setting myself? I ain't the swiftest with a volt meter - continuity and voltage is about all I'm good for.

The question comes from trolling cranks for the first time. I'd prefer to go off the TM in order to control speed better, but my batts ran down starting about 2 hours into it. Against my own advice, I installed a second batt of a different brand and slightly different age and quality (ie I cheaped out on the second one) when I purchased my boat. I just couldn't see scrapping 2 perfectly good batts just because they were different brands and slightly different in age by a couple of months - both only 8 and 10 months old with little use. But for my cheapness, now I'm not sure what's taking me out of the game 2 hours in - capacity or age on the batts.

Thanks for the help.

Wannabe...

You can't measure the current with a meter. The motor is turned on and off very rapidly to control speed, so the current will be a series of pulses. The pulses happen too rapidly for a conventional current meter to measure. I'd say at 40%, you could guess that you could run about the RC of one battery if they were new. For group 27 batteries, that's usually around 180 minutes.

Get away from the 27 and replace them with 29 s and you will like them much better.

Whoops, I said Group 27s, but I actually have 29s. That's the max size I can shoe horn into my battery compartment and had to do some engineering to accomplish that. There's no way to go to 31s without moving them forward and I really don't have any place to put them short of the front storage boxes....I think the performance of my boat would suffer greatly with that much weight forward. Guess I ought to start saving my pennies for the Optima or AGM batteries for replacements. I understand that both of them are smaller and the group 31s measure about what the 29s do.

Wannabe...

If you have an on board charger make sure it will support AGM batteries of you go that way. Personally I would go with the Optima.

Originally Posted by Wannabe...

Guess I ought to start saving my pennies for the Optima or AGM batteries for replacements. I understand that both of them are smaller and the group 31s measure about what the 29s do.

Wannabe...

Optimas are very small capacity batteries. 153 min RC vs. over 200 minutes for some bigger lead acid batteries (Everstart Maxx 29s and Trojan SC225s) or around 180 minutes for typical group 27 batteries. If you are already limited on your run time, it will probably be shorter with the Optimas.

Hmmm, I know Trojans are top notch, but was thinking the Optimas were up there too. Guess I'll have to break out the BWB battery blowout article and study up a bit. 'Course, I could always just take the rear hatch cover off and plop 2 honkin 31s in there and run like the rednecks do around here when they hop up a truck. LOL. Maybe I could rig up a fake Super Charger intake to really set it off.

Wannabe...

Originally Posted by Wannabe...

Hmmm, I know Trojans are top notch, but was thinking the Optimas were up there too. Guess I'll have to break out the BWB battery blowout article and study up a bit. 'Course, I could always just take the rear hatch cover off and plop 2 honkin 31s in there and run like the rednecks do around here when they hop up a truck. LOL. Maybe I could rig up a fake Super Charger intake to really set it off.

Wannabe...

Optimas are good batteries. You can abuse the heck out of them and they'll keep going. They charge fast, hold the charge for months without recharging, and last a long time. But they just don't have a high capacity.