Re: Which Battery to Buy?
 

Adam, can you comment on relative profit margins of battery production, when selling wholesale? If not, that's cool too.

Re: Which Battery to Buy?
 

The problem with a custom battery is you would have to provide it world wide. Including places with difficult customs laws. I think custom in a FRC sense would be standard cells in a custom case. Much different & simpler than designing from scratch.

A possible first step would be running them in a off season competition where the rules are little more relaxed?

Re: Which Battery to Buy?
 

Guys,
We do semi yearly checks with a CBA III analyzer and some of our batteries are still performing well from 2012. Some (one) from 2014 failed. Not all batteries get the same usage all year long as hard as we try to rotate.
Last year we were at 2700 teams +/- with about 400 rookies. But we all know of some really good teams that simply will die each year. It is part of real life for us. Some great people will step away, retire, change jobs or school districts will decide to spend money in other places. It happens.
Under our use, I estimate we should get around 400 charge/discharge cycles. Some teams more than that. As Frank mentioned, we are international and what is common and not so expensive here can be 50% higher just across the border in Canada or Mexico and may be considered hazardous in Israel or Europe. We also have to consider traveling and air transport of these devices.

Re: Which Battery to Buy?
 

That is what I have been attempting to suggest. Don't reinvent the wheel. Just make it better!

Re: Which Battery to Buy?
 

We also seem to get about 2 seasons (some more, some less) before we see the batteries start to fall off also, it's important to check. We load test with something similar to this:

http://www.amazon.com/gp/aw/d/B000AMBOI0?cache=cf334507e5e6604863e134ace7b1c657& pi=SY200_QL40&qid=1412860949&sr=8-1#ref=mp_s_a_1_1

We compare the voltage drop under load of the batteries and classify them as competiton or practice. This has worked well for us for a number of years. We can check them in a few seconds at competition also.

Re: Which Battery to Buy?
 

I purchased that exact model a while ago to run some tests. In my tests it did not detect weak cells:

http://www.chiefdelphi.com/forums/sh...44&postcount=4

Re: Which Battery to Buy?
 

I have seen that discussion before. Agree capacity testing a couple times a year would be even better.

How many batteries you try before finding one that can pass high load test, but fail capacity? Is capacity fail first more common than high load fail?

Re: Which Battery to Buy?
 

For practice, we've run deep cycle marine batteries that are used in our school electric car team. They work very well, but they have a different internal resistance than our FRC batteries, so the robot behaves differently. This is noticeable in autonomous mode.

Re: Which Battery to Buy?
 

Since we know the types of batteries this year, are there any that you would/ would not recommend?

Re: Which Battery to Buy?
 

As testing batteries came up... Attached is some sample code and a quick writeup on how to perform a full battery capacity check using equipment from the 2015 KOP and under $40 in resistors. I had two of our students code this up quickly so we could see which of our batteries need replacement.

Re: Which Battery to Buy?
 

Here's a home-brew battery tester if you can't spare $40 or you don't want to use your KoP PDP:

http://www.chiefdelphi.com/forums/sh...8&postcount=12

http://www.chiefdelphi.com/forums/sh...8&postcount=33

Re: Which Battery to Buy?
 

Don't trust the Battery Beak too much. We (Bomb Squad) have a CBA (Computerized Battery Analyzer) which drains the batteries to dead, 10.5 volts, and measures the amp hours. This is very accurate as it measures the whole life of the battery whereas the beak only applies a very small load for a very short amount of time. This makes it very inaccurate and right now we are working to find a correlation between the CBA and the Beak and post it for use. I hoped this helped in some way.

Re: Which Battery to Buy?
 

I wouldn't call the Battery Beak "very inaccurate". Of course the CBA is a better test, but the Battery Beak is accurate enough for its purpose, which is to quickly determine the state of batteries at competition. The CBA's test takes upwards of a few hours, the Battery Beak's test takes only a few seconds.

Re: Which Battery to Buy?
 

Our team has used the Genesis for our robot since 2013 and haven't had any problems with it holding a charge

Re: Which Battery to Buy?
 

Sean,
The only way to correlate the two is to set the CBA to the same load. The Beak uses two resistors one a very light load and one a heavier load and then makes a calculation based on tested impedance and displays the result of the calculation.