GEM Battery Engine Sizes and Load Test for Batteries

I could really use help in gathering information of the current or amps that a gem motor draws while under load as I trying to get a new BMS system and come up with a 72V option to run parallel for the longest and most dependable battery run times. I have a few suppliers that need the info and are ready to build based on the specs I give them.

Any help would be greatly appreciated as I have been using them on a much simpler scooter and ebike applications. I had them do batteries for some scooters that used to run 11-12 miles. Now with the new batteries, my kids are getting 60-70 miles and the batteries have been performing flawlessly.

I want to be able to determine the best cutoff range and information like GEM motor watts compared to HP as they are not familiar with HP as its more standard for them to build based on watts and max current draw etc.

Thank you to everyone for helping as this is a project that I will share and be able to offer whatever setup we build to other GEM owners without the crazy price tag all the lithium offerings currently have.


Been there done that! :slight_smile:Look thru the lithium threads.
The work has been done for you.
Hp to watts is just math.
Current depends on voltage. 300a max should work for anything.
Gem won’t start below 68v or over 85v, but will run down to 62v or so, and up to 100v.
Use 150-250 w/h per mile.
Minimum battery should be 100ah. I’ve run on a 11ah LTO jump pack as a test.

Still trying to determine how many watts the GEM motor is and the max dischareg rate for the batteries.

3730 watts is 5hp.
What batteries do you need the max discharge rate for?

The max discharge rate for my battery setup is around 160amps, just want to make sure its overkill as one of my other gems has the aftermarket motor 7.5 HP and 11 Peak HP. I’m hoping the new battery options will be strong enough for either setup. As they are lithium 72V 100ah batteries run parallel to make a 72V.

Do you know how many watts the high power motor is I have in my other GEM?

7.5 HP and 11 Peak HP = Watts ??

Thank you for the reply.


If you connect 6pcs or 12V 100ah batteries in series to make 72V does it make the ah 600?

No, 100ah.
Are you sure you want to get in the battery biz?

Joe ,

If you dont know this you are way over your head , this is basic electrical knowledge .

on my gem with a 84v lithium pack in it , it will surge to 350 amps on full acceleration . once at 36 mph it runs between 95 to 110 amps . this is on flat ground , on hills it will go much higher . this is also with a 5hp motor.

so it will depend on how you have your controller programmed , what top speed you are running , your load (weight and hills) and size of your motor .

my guess is if your running a low voltage of only 72v then your cart will pull high amps under load . easily over 300a to start then might be just below 200 amps continuous . A guy like Grant that is running 95v probably pulls closer to 100a continuous .

you can buy a $15 meter , hook it to you stock pack and take a drive , it will tell you what your cart in your condition needs .

p.s. when i design packs i want them to be fully charged around 85v and have most of their capacity between there and 70v , under 70v gems are dogs.

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So to have 600ah I would need to run something like 6pcs of 72V 100ah batteries in parallel or close to that?

Thank you for the response and I have already run a few different 12V 100ah systems over the years and had a few BMS problems and everyone says its much easier to just run 6pcs of 72V 100ah batteries parallel as they are more stable and last longer. Appreciate the responses and hope to make some progress with all your help.


Just the opposite.
Wiring 6 banks of 20 or more cells in parallel is a nightmare. 21 wires to each of 6 batteries is crazy.
Is there something new you want to try?

I was just looking to wire 6 batteries in parallel using batteries the same size as the factory setup in the GEM to have a less maintenance system. The only thing that seems to be different is the 72V 100ah batteries are a bit more in cost.

What is hard about wiring 6 batteries in parallel?

A bit more?
Where will you find 72v 100ah for less than $1k each?

As in previous reply, it takes 20s minimum for 72v battery.
That means 21 leads from each one.
Picture shows 2 72v in parallel.


Sourcing is not the problem. I’m just trying to get the specifics of what I need so I can have my suppliers build what I need. I appreciate all the responses to help me develop a dummy proof setup. I am getting all the quotes together now and for the batteries. I am having 6pc sets of 12V 100ah batteries and 6pc sets of 72V 100ah batteries quoted. I am not going back down the road of installing 3.2V 120ah batteries as it’s not practical for the end users.

Please keep helping and sharing any information as I will share my results as the project progresses.

I am also thinking of all plug n play connection from battery to battery as well to make it a straightforward installation.

Feel free to ( constructively ) chime in with any info or details that you think will benefit the outcome of the project.

Thank you, Joe

What is target price for these 600ah battery kits?
Lipo? Life? How many cells/volts.