Nimh vs lithium ion wic to prefer for gopigo

share thots pls not expert.
need to buy.

Two reasonable options are 3SP1 Japanese Li-ion, or 8 Japanese (Eneloop) NiMH AA cells.

I prefer the NiMH as safer for an indoor robot.

My tests of Chinese NiMH and Li-Ion 18650 cells and 12v “ BMC 3SP1 packs” proved disappointing due to inflated capacity and cycle life claims and vast quality differences batch to batch of the same brand.

Recommend 1900 mAh NiMH AA cells which will provide 5-6 hours of Raspberry Pi 3B (non-plus) development time and around 2 hours of drive, think, drive some more time. Generic 1900 mAh cells are more consistent than 2600-2800 mAh cells so may be acceptable but I am very pleased with the Eneloop brand cells,both high capacity “pro black” and now the “white 1900” cells.

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One thing I always say is that the choice of battery technology is influenced by several considerations:

  1. Capacity.
    Can it deliver the advertised capacity?  Is the run-time adequate for your needs/requirements?  Note that though capacity and run-time are related, it’s not a strict relationship.  Depending on a number of factors, not the least of which are manufacturing techniques and the actual, (proprietary), chemistry used, the ratio between capacity and run-time can vary greatly.  As @cyclicalobsessive said above, higher quality batteries give longer run-time.  Also note that “name brand” batteries are not necessarily the best or the highest quality.

  2. Size/weight.
    This affects both capacity and run-time.
    This also affects center of gravity, overall balance, traction, accuracy of motion, etc.  With respect to weight, there is a “sweet spot”, (determined experimentally), where you get the best traction and accuracy without excessively affecting the center of gravity and balance.

  3. Battery chemistry.
    This will affect both of the above.

    • Lithium/LiPo batteries have a higher current density per weight ratio - you can get a lot of current from a much lighter battery than with other technologies.
    • Any lithium technology requires close examination of the relevant spec’s regarding both charging and discharging.  This is actually true for ANY  chemistry you may wish to use - it’s just that lithium battery technology is relatively new and it’s easier to get batteries and/or chargers that don’t meet the spec.  Again, as with everything else, shop carefully and only deal with reputable suppliers that have a track record of competence and care.
    • NiMH technology is “safer” in the fact that the technology is more mature, and it is, (relatively), easy to get batteries and chargers that meet the specifications.  Beware!  Not all NiMH chargers are created equal - some chargers aren’t smart enough to know when to stop.  As a consequence the batteries can overheat, explode, and/or catch fire.  (Of course, this is true of any battery chemistry - lithium and lead-acid, (gel-cells), are also notorious offenders.)  Don’t get the cheapest batteries or charger, get both batteries and charger that are good quality and - especially with the charger - get a “smart charger”.
    • Lead-acid, (gell cells), can give you the highest current density and a correspondingly increased run-time - but at the expense of a LOT of excess weight.  Additionally, gel-cells are just as picky about their charging profile as lithium or NiMH batteries - feed 'em too much current and you have a Real Problem on your hands.
  4. Your own personal preferences, your budget, and the requirements of your particular application.
    This is, by far, the most important consideration.  If you are afraid of a particular battery technology/chemistry, then by all means don’t use it.

The real bottom line is that both your requirements and preferences - with a knowledge of the pros-and-cons of each battery technology - will allow you to select what you need.

In my case I also use NiMH because I have not found a lead-acid battery with the requisite current capacity that doesn’t require a fork-lift to carry - :wink: - and lithium battery technology is much more fussy - batteries have to be carefully matched and charging has to be carefully distributed across all the batteries in the array.

Note that this is also true for arrays of NiMH batteries, (or any other battery chemistry), but since in most cases people use individual “AA” size batteries and a charger that handles the batteries individually, this is less of a consideration.

Do your homework, check the batteries available to you, and let us know what you decide.

Jim “JR”

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