May 6, 2009

Battery Discussion

A few week ago at WorldFest, Steven with LEGO handed me three packages of Energizer Lithium batteries (2 per package)... he said "try these out."

I put them into my brick that I'm using for testing robots in a new book (where I'm constantly stopping, starting, stopping, etc.) and decided to see for myself. Having used a mixture of alkaline and rechargeables in the past, I have to say these things are unreal... I'm still using them after about 2 weeks of daily use and they're still showing 8.X on the battery meter. I've seen no change in performance either.

They're a little higher priced than the batteries I'm used to using, but for testing purposes, I'm really leaning towards switching over to these during those critical testing periods. It made me think of FLL teams who are also constantly testing and need reliable batteries.

I'm interested to hear from our readers on their battery experiences. For those who don't use the NXT rechargeable, what kinds of times are you finding on the batteries you use? What do you use?

8 comments:

Alan LeVezu said...

There's no question. Energizer E2 Lithium are THE battery for an FLL team. The expense is also unreal typically at least $2.50 each... that means that commonly you will spend at least $15 per set for the NXT.

The Lego Guards team uses them at competition, and for two weeks before. (As a teaching experience, I have them look up the voltage drop curve at http://www.powerstream.com/AA-tests.htm to see what the cost vs power thing is all about.) Actually the hardest thing to deal with on these batteries in FLL is that they are so powerful that the robot overreacts for the first hour or so of use... That being the case, we also NEVER put new batteries in the day of contest - only the day before! Last year at world, we did not change batteries once...

Dave Parker said...

For projects that I post on nxtprograms.com, I intentionally develop and test with worn alkaline batteries, so that I don't accidentally post a project that depends on fresh batteries. Sometimes I err on the other side, though, and make one that depends on worn batteries to work well...

I have a steady supply of worn alkalines from our school robotics club which uses the RCX. I tried rechargeable AA NiMhs for a couple of seasons in the past, but those don't last long at all between charges (they leak even when not used too), so you have to swap constantly, which is a pain. So now I buy big packs of cheap alkaline AAs from Costco ("Kirkland" brand) for the school club, and those will last the whole season (about 15 one hour classes). Then I take them home and use them for my NXT projects until they are very low. Then I take them to the recycle center and hope that "recycle" actually means something on the other end (BTW, I hear that Lithium batteries are better for the environment too).

One note on battery level: The way alkalines work and the way the NXT's little battery icon on the NXT display works, just because the battery icon shows full, that doesn't mean anything when the NXT is idle. You need to watch the battery icon while giving the motors some load (it will dynamically update and you can watch it fall as the load increases). How much the voltage falls under load is a much better indication of remaining strength of the battery. The same thing applies to the NXT-G battery voltage display on the PC if you are connected (which is of course much more accurate than the icon on the NXT).

For my FLL teams, we use the rechargeable NXT pack for simplicity and consistency. I would recommend this for most beginner/intermediate teams. That is, unless you make it to the finals and need to race Alan's team to the center mission...

Finally, note that if you swtich battery types mid-season, be prepared to re-tweak all your programs, the amount of wheelslip may change considerabley, if your team's robot is prone to that (may be more so than you think).

BlueToothKiwi said...

Your robot and the Energizer bunny has a lot in common.

I don't know if you remember whe first NXT was launched, LEGO ran a promotion with Energizer E2. You buy a NXT kit - and you get a free E2 power pack (made up of a pack of Energizer E2 Lithium batteries and some extra NXT sensors). And they were FREE !!!!

We should talk to LEGO about repeating a deal like that with NXT 2 later this year!

Tim

jbrost76 said...

I stick mainly with the rechargeable LEGO packs simply because they're cheaper to operate over the long haul. However, when I compete in LEGO sumo matches, I almost always throw in a set of E2 Lithiums. Beyond lasting almost forever, since they operate at a slightly higher voltage than regular AA batteries, they provide a little extra power. And they're much lighter. When you're trying to get a robot that weighs 1.1 kg in under a 1 kg weight limit, every gram counts. I've used that trick more than once, swapping regular AA batteries for e2 lithiums instantly transforms an overweight robot into one that makes the weight limit :)

John

Brian Davis said...

Like John most of the time I use the Li-ion battery pack - I can recharge it, it's light, and I can run it straight from the wall if I want. But like any job, there are times using the right tool is important...
...if I need to reduce weight (overweight sumo, balloon missions), I pop in a set of Lithium E2's
...if I need to run reliably a long time (datalogging over 12 hours or more), I use E2's.
...if I need a little bit extra power, (overvoltage, stronger motors), I use E2's.
...if I need to run under very cold conditions (in the freezer, or balloon missions), I use E2's (the work to amazingly low temperatures).
...if I need to save money... I AVOID E2's. They are really good, but (like anything else) only worth the extra cost in the specific situations where you need their more unusual abilities.

Thas said...

Thank for a very detailed discussion on batteries for NXT. My teams were using Energizer (or Duracel) alkalines until last week. Then we introduced Energizer Lithium... Performance was amazing. But we noticed that the NXT failed to turn on the motors at least once (even though the program was running with the circular icon rotating in the screen). Could the Lithium's total voltage (which seems to be close to 9.5V when fresh) be too much for the on-board voltage regulators? I would suspect this not to be the case. But I want to know if others saw such erratic behaviour of electronics. I do understand that the robot will be a bit 'jumpy' when the batteries are fresh.
Thanks.
Thas

Thas said...

I have one more clarification about Energizer Lithium (disposable) batteries: My team is using firmware version 1.29. Is the NXT brick designed to report voltage levels assuming the power source is alkaline? Parameters used in estimating voltage levels is dependent on the battery chemistry. I turned the NXT brick with Lithium cells a day after full day of testing by the kids. The reported voltage was 10.0V !!!! The day we installed the batteries, the reported level was 9.5V. This seems strange. Any and all pointers will be much appreciated.
Cheers,
Thas

Beda Bogdan said...

I know there's been some time since this post was discussed but it's worth giving a try. Right now I am using GP1600mAh wich I recharge for 16+ hours to get 10 minutes of testing. I CAN'T use my NXT. I see from this post that those batteries don't last very long. I don't like the idea of using alkaline batteries for testing and playing because the costs can go high if you sum them up in time. How reliable is the NXT Rechargeable battery anyway ? Does it worth the high cost ? For how long can you start/stop programs before you must recharge and how long does it take to recharge ?

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