Internal battery resistance values

From another forum thread I have been reading “Your Team Sucks at Electronics: Here’s Why”, I read that batteries with internal resistance over 0.02 ohms are not suitable for use. Does this value apply for competition use or regular testing use?

We use FRC 12 volt sulfuric acid batteries, a link provided: http://findrobotparts.com/batteries/
(First and third from top of list)

Thank you in advance.

Batteries over 0.02 ohms could still be good for testing depending on what you are doing.

On 2910 we don’t use batteries over 0.017 ohms for competition.

Remember that if you are measuring internal resistance with a battery beak you are also measuring the resistance of the wire, connectors, crimps, and connections. So it may not be a bad battery but instead one of those other items needs to be fixed/improved.

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For normal day to day use, what range of internal resistance does your team usually use?

Anything from 0.013 ohms to about 0.023 ohms. Anything over 0.023 ohms isn’t worth keeping for us.

Now days we usually get like 8 new batteries each year so if we don’t get rid of our bad batteries we end up collecting way to many of them. We buy batteries direct from MK battery for about $35 delivered.

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The place where we get our batteries cost around $80 per battery. Is it possible for you to post the link to the $35 battery site?

https://www.mkbattery.com/

Give them a call and tell them you are an FRC team. They will set you up.

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As CptJJ said just give them a call to place an order. I’ve paid by card over the phone with them before and have gotten a receipt emailed to me.

I found the MK batteries even cheaper here. We have not actually ordered from them yet. I was just doing some research to do a battery buy this past weekend when I found that source, so I can’t actually give you a review.

The word “replacement” in the product listing leads me to believe this is not actually an MK battery.

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I was a little suspicious as well. That was one of the reasons that I didn’t purchase it.

Ordering directly from MK is the safest option.

It seems like the website is mainly specializing in replacing batteries. They also have batteries for scooters, snowmobiles, go karts, and motorcycles.

But I see there are plenty of good reviews as shown here: https://www.trustpilot.com/review/batterysharks.com

I have another question: which battery terminals do your team use to connect to the leads of the batteries?

We use a terminal that breaks quite easily, as the connections between the parts of the terminal fall apart as time progresses.

The end of the cable is the “terminal” part of the battery I am referring to, although we do not use this type of terminal.

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I’d still be cautious. I wouldn’t be surprised if they just send a battery that’s the right size, shape, chemistry, and voltage but still isn’t MK brand. Most of those reviewers are using those batteries for boats and motorcycles and stuff instead of for robots.

6 AWG ring terminals, similar to (and sometimes exactly) the ones in the KOP.

This year our best battery had an internal resistance of 14.76 mili ohms at the end of the season and by looking at our battery testing report at Click on our battery report tab by using this method we are able to determine the best from the worst batteries and that proved to us that the KOP battery was the worst battery we had. Also, our best batteries are Duracell and this years best was brand new

I did not see this thread until today. For starts, the manufacturer for each of the legal batteries specifies a slightly different internal impedance, not resistance. This is typically 0.011 ohms for a charged, new battery. Poor crimp terminals, loose hardware and dirty terminals on the battery can all add to this number. BTW, #6 wire is approx. 0.0005 ohms per foot. Impedance is also subject to internal temperature and the frequency of the test instrument. Internal impedance is normally measured with a fully charged battery that is at room temp for a few hours after charging, measured at 1kHz.

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We have seen this first hand. When the couple batteries we are using at an event are getting a good workout and getting warm it is not uncommon for us to see them at 0.012 ohms on the battery beak and over 13v on the driver station when we are waiting for the match to start.

This is normal for a battery that has just come off the charger. It is called “surface charge” and will rapidly go back to 12 volts once a small load has been applied.